Do we really eat spiders in our sleep?

Urban mythology claims that each year, a certain number of spiders crawl into out mouths while we are asleep and are consequently eaten. While the exact number of spiders that we are supposed to eat varies widely, the common theme remains the same and the stories usually suggest that there is nothing we can do to prevent this from happening.

Spider silk is one of most amazing chemicals in nature, being both incredibly light and having a tensile strength that is far greater than steel. In fact, the silk of the golden orb weaver (not shown above) is 6 times stronger than steel and is 10 times more efficient at absorbing energy than military-grade kevlar, being tough enough to capture bats and small birds!

Whereas it is doubtful that we could stop spiders from crawling or lowering themselves into our mouths if they wanted to (we are asleep afterall), there is actually no need as a spider would not be interested in creeping down our throats, so that in fact, we have nothing to worry about whatsoever!

This is mainly due to the content of our breath, which is warm, humid and has a much higher carbon dioxide to oxygen ratio than 'normal' air does. If a spider was crawling towards our mouth, it would sense such conditions when we breathed over it and would actively avoid them since they signal that the conditions within are mouth are harsher than those outside. Imagine, for example, smelling smoke coming from your living room - even if you couldn't see or feel the flames, you would know that something was wrong and that there may be a danger in the room. Thus, you would most likely avoid going in!

For similar reasons it is unlikely that a spider would want to enter your mouth and, if one was on your face, would probably turn tail and run once it came close enough to feel your breath!

Do our hair and nails really grow after we are dead?

Many people will tell you that once you have died your hair and nails will continue to grow for days afterwards, with the exact time period varying depending on the individual telling the story. This popular piece of 'common fact' is undeniably interesting, but sadly, is completely incorrect; being nothing more than a frequently repeated tale of urban mythology. To put it simply, when you are dead your metabolism has completely ceased and among many things, this means that your body cannot create any new material like hair and nail tissue.

This is an electron micrograph of a human hair follicle. Hair is formed from rapidly dividing skin cells that are killed almost as soon as they are formed and filled in with a insoluble biological 'wax' and colouring pigments. They are then wrapped up a bundle of keratin fibres to form a helical strand of hair. The strand then grows from its bottom as new cells push the older ones upwards. Nails grow in much the same way, except they are laid down in sheets rather than as a helix.

Yet despite this, a deceased person's hair and nails do appear to grow for nearly a week after they have died... Although this may appear confusing at first glance, the answer to the conundrum is in fact very mundane: the human body is predominantly composed of water and over time, a cadaver dehydrates. As the cadaver looses water into the surrounding environment, their skin contracts and exposes already grown (but previously hidden) hair and nail tissue. It is surprising how much of these materials your body has tucked away beneath your skin and, by contracting, gives the impression that they are eerily growing post-death on their own accord...

Dehydrating skin also explains another common feature of corpses, whereupon they appear to smile. As the skin around their mouth becomes tighter it contracts and pulls the lips away the mouth, giving the impression of a somewhat grotesque smile.

Thus the simple action of water moving out of our bodies after our death has instigated confusion for hundreds of years, giving rise to a popular story that many people incorrectly believe as fact!