(Video Link)
YouTube user thearchipelago went frog gigging and brought back these three whoppers. When he adds salt to the raw meat, they start twitching wildly. Why does this happen? Marshall Brain of How Stuff Works explains:
Because these are fresh frog legs, the cells inside them are all still intact. The biochemical machinery still functions. There is still a source of energy for the muscles in the form of unused ATP molecules stored in the cells. All that the muscles need is something to activate them and they can still contract and relax (until they run out of ATP or something else shuts down the biochemical machinery).
http://blogs.howstuffworks.com/2009/12/21/how-twitching-frog-legs-work-a-little-gross-yes-but-fascinating/ via Geekosystem
http://tywkiwdbi.blogspot.com/2010/06/headless-skinned-gutted-fish-wiggles-in.html
The wild elephant is another topic entirely and at least that story had an element of survival for its event.