For some reason, I woke up this morning wondering about the evolutionary advantage behind the second tongue-mounted head inside the mouths of Ridley Scott's Aliens. Thankfully, Ed Yong of Not Exactly Rocket Science, was already on top of this conundrum, offering an earth-bound analog—the moray eel.
Moray eels use a ballistic set of second jaws to catch their prey. These 'pharyngeal jaws' are housed in the eel's throat. When the main jaws close on an unlucky fish, the second set launches forward into the mouth, snags the prey with terrifying, backward-pointing teeth and drags it back into the throat. In fractions of a second, the prey is bitten twice and swallowed.
The adaptation allows long slender eels to pop out of their rocky hidey holes, and quickly catch and hold wriggly prey.
