Yo-yo

A yo-yo is a toy, often wooden or plastic, composed of two wheels on a fixed axel around which a string is tied. It is operated by using gravity or force from the user's wrist to unwind the string, then jerking it back once unwound to rewind it. This originates from a weapon used in Hawaii before North American colonization, though is now (generally) far less dangerous, and most often the yo-yo is used as a toy for relaxation.

The Fourth Doctor rather enjoyed playing with the yo-yo he kept in his jacket. (DW: The Android Invasion)