Is the exterior of a soap bar always clean?
-> No. After use, soap has a film of water, soap and dirt left on its surface that dries out to leave the dirt stuck to the soap.

If you throw water in the air in the Russian winter, will it come back down as ice?
-> Yes. A cloud of water droplets at -30°C will fall to the ground as particles of ice.

What is ‘pins and needles’?
-> This is a form of paresthesia that is similar to, but milder than the feeling of a limb ‘going to sleep’. It can be caused by poor blood circulation but in healthy individuals it is more normally caused by compressing the nerves that run past the elbows or knees. This interrupts communication with the sensory nerve endings in the hands and feet and when the pressure is released the nerves suddenly begin firing wildly and randomly until a sensory threshold is re-established. It is normally very transient but certain medical disorders such as diabetes or hypothyroidism can cause chronic pins and needles.

Why do onions make you cry?
-> The action of cutting an onion releases a fine spray of droplets. Recent Japanese research has shown that these droplets contain an enzyme called lachrymatoryfactor synthase and sulphur-containing compounds, which react to produce a powerful irritant called Syn-propanethial- S-oxide. When a droplet strikes your eye, you respond by producing a copious flow of tears to try and wash the irritant away.

What happens to cells in our bodies when they die?
-> Cells on the surface of our bodies or in the lining of our gut are sloughed off and discarded. Those inside our bodies are scavenged by phagocytes – white blood cells that ingest other cells. The energy from the dead cells is partly recycled to make other white cells.

Do left-handed people think more laterally?
-> No, there are no studies to suggest the creative ability to see unusual or surprising solutions to problems varies between left- and right-handers

Can we correct colour blindness?
-> No, colour blindness is caused by an inherited defect in the genes that code for the colour-sensitive proteins in the eye.

Do any stars escape from their galaxies and roam through the Universe?
-> Yes, a star can end up hurled out of a galaxy after approaching a black hole on a trajectory that accelerates it above the galaxy’s escape velocity.

Does the size of your head affect your IQ?
-> No, a 1998 study concluded that there is a correlation between head size and brain size, but that IQ was not related to size, at least not in young, healthy adults.

Can the government track you if you have a GPS-enabled mobile phone?
-> Yes, if your phone has GPS, your location could be relayed to an operator, but you’d have to be on the phone to them.

How are birds’ feathers waterproofed?
-> Birds pick up oil on their beaks, by rubbing against the uropygial or preen gland near the tail, and then rub it over their feathers. This coating insulates the interlocking barbules in the feather. As water cannot penetrate through the oil coating, the feather is waterproof. LV

Why are lobsters cooked alive and do they feel pain?
-> Lobsters and other shellfish have harmful bacteria naturally present in their flesh. Once the lobster is dead, these bacteria can rapidly multiply and release toxins that may not be destroyed by cooking. You therefore minimise the chance of food poisoning by cooking the lobster alive. That’s great for us but what about the lobster? It has been argued that lobsters do not possess a true brain and so can’t feel pain. It is fair to say that they are not self-aware in the same way that we are, but they do react to tissue damage both physically and hormonally, so they are obviously capable of detecting pain on some level. In fact, the hormone that they release into the bloodstream, cortisol, is the same one that humans produce when hurt. But the most visible sign of distress is the twitching tail, which evolved as an escape reflex. Researchers at the University of Maine found that putting the lobster on ice for 15 minutes before dropping it into boiling water produced the shortest tail-twitching interval (20 seconds). Contrary to the popular urban myth though, placing the lobster in cold water that is then slowly brought to the boil does not anaesthetise the animal and appears to extend its suffering.

Why don’t spiders get stuck in their own webs?
-> A spider’s web is built like a bicycle wheel, with an outer rim and spokes running to the centre, and then a spiral from the centre back out to the rim. The spiral is the only bit that is coated with glue – the spokes and outer rim are made from dry silk. The spider mostly avoids the sticky sections as it moves and it has very minimal contact with the web, in any case. On top of this, spiders constantly groom their legs to keep them clear of silk and glue.

How high must you sing to shatter a wine glass?
-> The note that a wine glass makes when you hit it is its resonant frequency – the frequency at which the glass vibrates most efficiently. If you can match this tone you can smash the glass. The note will be around one octave above middle C, depending on the size of the glass. The real trick is singing loudly enough. Even with expensive,glasses, which vibrate with a clear tone that doesn’t damp down quickly, the amplitude required is at the limit for the human voice. An untrained singer can do it relatively easily with good amplification but achieving the same thing without a speaker has only been done once on TV, by singer and voice coach Jaime Vendera for the Discovery Channel’s Mythbusters show.

What would happen if there were no Moon?
-> The most immediate effect (other than the lack of moonlight, of course) would be on the Earth’s tides. With only the Sun’s gravitational influence, the difference between high and low tides would be reduced dramatically – as would tidal drag, which slows the Earth down at a rate adding about 0.002 seconds to the length of a day each century. Long term, the effects would be far more serious. The climate of the Earth is sensitively dependent on the 23.5° tilt of the Earth’s axis, and without the stabilising presence of our relatively huge Moon, the gravity of the other planets would produce big changes in this angle – as it does with Mars, whose tilt changes by 60° over a few million years.

Why do drugs have a shelf-life?
-> Cynics argue that shelflives are just invented by pharmaceutical companies to make us buy fresh batches of perfectly good drugs. In reality, government regulators demand extensive testing to find out how long the compounds retain their potency. When they’re kept at room temperature, the molecules that make up the drugs degrade just like foodstuffs – and can, in some antibiotics at least, even turn toxic. RM

Why do your eyes water when your nose is hit?
-> The nose is soft and sensitive, and the nasal passage is connected to the eyes via the tear ducts. Normally this allows the lacrimal fluid (tears) to drain through the nose. But when the fluid build-up in the nose is sufficient, the flow can block the normal draining path, so that the tears that are produced have nowhere to go.

Why do humans cry?
-> We produce three different kinds of tears. Basal tears lubricate the eyeball and make it optically smoother. These are produced continuously at a rate of almost 300ml a day. Reflex tears are produced in response to physical or chemical stimulus and wash away irritants. The third kind is produced in response to high levels of emotion. This stimulates the cranial nerve in the brain, which sends neurotransmitters to the lachrymal glands. It also raises the blood pressure in the face, which tends to increase the flow of tears. Emotional tears contain high levels of manganese and the hormone prolactin (which normally stimulates the mammary glands to produce milk). Humans are the only animals that cry in this way and it has been suggested that emotional crying may have evolved as a way to remove excess levels of certain chemicals and only later became ritualised as a way of signaling emotional distress.

Can dock leaves really sooth nettle stings?
-> No, the myth of dock leaves soothing nettle stings arose because of parents’ desires to find something close by with which to placate their stung child.

Read the full 101 Greatest Questions of All Time in the March issue of BBC Focus. Find out more at www.bbcfocusmagazine.com

101 greatest questions of all time: 1-20
101 greatest questions of all time: 21-40