I have heard the phrase internal clock many times before and was wondering if there was any scientific explanation as to why we feel the urge to sleep when its dark(night).

When talking on either a hands free phone or a mobile, I have a tendency to aimlessly wander around the house, as do many other people I have talked to about this.  Why is this?  What is it about talking on a phone rather than face to face that makes you subconsciously want to wander?

The blue-footed booby is an extraordinary-looking bird. It has fairly dull plumage but strikingly coloured blue legs and feet. What could be the evolutionary benefit of such a conspicuous feature? Both sexes have blue feet so they don't seem to be for impressing potential mates.

Do birds ever collide? If not, why not?

Birds do collide. Thanks to all who wrote to tell of clashes between various species. Interestingly, nobody reported evidence of collisions between birds that fly in formation, such as starlings. From an evolutionary perspective it would seem to make sense for flocking birds to have collision-avoidance systems - Ed

Why do we have an instinctive tendency to hunch our shoulders when walking outside in cold and rainy conditions?

Stephen Barker, UK

Since we have such different faces and body structures compared to dogs, how can they instinctively tell that the two spots on the upper portion of our faces are in fact our eyes, and not, for example, our nostrils?

Dogs seem to understand the concept of 'names' more than other animals.  My dogs know the names of the cats and recognise their own names.  Does this mean that they have a similar system themselves or merely associate the sound with the image?

I can understand how sound + image works in the case of the cats names for example, not sure how it would be applied to their own name though.

Is it a myth that cats only purr when in the company of humans? Or do they purr when on their own as well?

Obviously they are nocturnal and diurnal, respectively, and have different roosting/nesting habits, but they do compete for many of the same food resources.

Has there ever been any observation of crepuscular turf wars or clashes? And if not, why not?

Whatever the answer it might still make for a fun (bad) made-for-TV sci-fi movie.

Why don't we do things that we know will have a benefit? Such as, saving up for a new pair of shoes, then going and spending your money on make-up instead, or choosing to have an extra packet of crisps, or choosing not to go on a run because we're 'too tired'. It's clear that all of these things are good for us in the long run, so why do we choose to do something that will only benefit for maybe a few minutes or so.