Whales...

Darren naish has three interesting posts about rorquals, i.e. whales which fill their mouth of water (and other stuff) to feed, such as the Blue Whales... the techniques is called lunge-feeding, and that's why these whales have such huge mouths... the adults blue whales' jaws, at seven metres each, are the largest single-piece bone of all animal world.

One, two, and three

:-)

edit: as Darren correctly points out, not all rorquals lunge-feed.

edit2: I once dreamed of swimming with whales off the coast of canada. It's been the start of my new life :-)