This week, you pit your wits against the Naked Scientists team and challenge us to answer your science questions. Is there an evolutionary reason why humans have rhythm? Do people sneeze in their sleep? Why do crabs walk sideways? And how do stinging nettles sting? Chris Smith, Carolin Crawford and Ginny Smith join Kat Arney get their teeth into your conundra, and take a closer look at the stories hitting the headlines, including a sieve that separates oil from water, how you can sniff happiness in sweat, and the Hubble telescope celebrates its 25'th birthday...