Quite the fad at the moment, Zhu Zhu Pets!
They're furry little toy hamsters that have little wheels so they can zoom around the floor and through their own little hamster track.
What makes them evil? Kids are kids, and though there is a tiny sticker underneath them saying not to put them anywhere near hair, kids will eventually put on on their or someone else's head. When that happens, the wheels which go like the clappers will tangle and snag the hair and the only way to get out of the tangled mess is by cutting the hair down to the scalp, either that or your kid freaks out and rips a chunk of hair off.
Seems to be quite a common theme, there's thousands of posts of this type of incidence happening all over the interweb.
Definitely not a toy for little kids, even though it does say over 4 year olds, I'd be sceptical about anyone younger than a teen playing with one of these and even then...