There's a river near us where crayfish can often be found sitting at the water line, eating the algae that grows there. If you drop a hook baited with bacon fat on one, he'll grab like crazy until he gets it, then he'll stuff it in his mouth and keep it. They hold on so tight that you can lift them three feet out of the water and onto the bank, and they don't let go until they slip off.
They won't do that with any other bait I've tried so far, though. They'll prod at most things, but it's only bacon they go nuts for. Why do they like bacon so much? Is it the salt?
Do shrimp and prawns have a similar reaction? I've never found any to try it with.