This isn't too surprising. Of course a system designed to recognize the ridges of fingerprints can identify the ridges of your lower appendages, too. Although, removing your shoes each time you need to unlock your phone seems like a bit of a hassle.
Various animal paws
This is the Internet, so of course someone tried to use cats -- and it looks like it works. Not to be left out, man's best friend (the dog) also seems to be able to set up a paw-based TouchID. Presumably, this would work for nearly any animal with paws, although good luck keeping a raccoon still long enough to get it working.
Don't worry, the video is safe for work -- unless you work in an office where manboob is deemed unsightly. Anyhow, a fairly legit-seeming video from Japan shows a man using his nipple to successfully unlock TouchID. So, if that's what you're in to....
Last, but certainly not least, German hackers said they were able to trick TouchID over the weekend, as my colleague Hayley Tsukayama reported Monday morning. Using a photo of the needed thumbprint, a laser printer and some latex milk, the Chaos Computer Club was able to fool the fingerprint scanner, the hackers said. If the hack works, it would not be a full break of the system, since it would still require access to a photo of the thumb print, but it certainly shows that TouchID may be far from foolproof.