What does an alligator sound like on helium?

Dr Stephan Reber and colleagues gave an oxygen-helium (heliox) mix to an alligator in an enclosed tank. The researchers were able to analyse the different sound frequencies in the animal's bellows to show how reptiles can communicate their body size through their vocalisations.

The work won the team one of this year's Ig Nobel prizes - the awards that are a comedic spoof on the more somber science Nobel Prizes announced in October.

Listen to the sound file on this page. The first pair of alligator calls are in ambient air; the second pair are bellows made in heliox.

Read more: Alligator on gas snaps up Ig Nobel prize