Welcome to this Friday's round-up of the week's top questions.

Ever been puzzled how you can blow both cold and hot air out of your mouth? purple2410 asked The Last Word, and got some very interesting replies.

A discussion on whether a body will use more calories and water if there is more available to it branched into the effect of weight on the speed of freewheeling downhill on a bicycle.

Here's one that has always puzzled me: how do fish get up to the top of a mountain?

Last Worder Milon has some ducks that are behaving strangely… they seem to want to play with their own version of a rubber duck. Can you explain why?

Finally, today's question gets to the lungs of the matter: what causes the burning feeling you get in your throat and lungs when you exercise beyond your normal capacity?

All the best,

Kat

Letters and comments editor, New Scientist