Snakes use sponge action to drink. (via Herp Digest)

2/20/12, New Scientist Magazine issue 2852. 

WHAT do a snake's mouth and a sponge have in common? Capillary action. Some species may use skin folds in their lower jaw like a sponge, to soak up water and ferry it into their gut.

In 1993, researchers found that boa constrictors sucked water in through a tiny hole in their mouths as if they were drinking through a straw. But David Cundall of Lehigh University in Bethlehem, Pennsylvania, found no evidence of suction when he placed pressure sensors inside the mouths of three other species, Agkistrodon piscivorus, Heterodon platirhinos and Pantherophis spiloides (Journal of Experimental Zoology, DOI: 10.1002/jez.1710).

Instead, Cundall thinks that skin creases in their lower jaw, which expand when the snakes swallow large prey, help them drink. Their tongues, he notes, are too small to lap up water, and are covered in a sheath that would prevent this even if they were larger. And snakes can't tip their heads back to scoop in water like humans do.

Instead, he says, the skin folds work like tiny tubes in a sponge, drawing water into the mouth through capillary action. Muscle action then squeezes the water down into the snake's gut.Kurt Schwenk at the University of Connecticut in Storrs is convinced. "How animals drink is surprisingly complicated. I think they've pretty much nailed it in snakes."