Everyone has a name for them: the excellent Phil Hawksworth calls them “delighters”, my friend Tom Knowles and I call them “showbiz coding.” They are little bits of UI that do something unexpected and fun.
I’m going to jump to my favourite kind: 3D effects. They give your UI some depth and, much as with the Spanish Inquisition, nobody expects those suckers. They also have the advantage of being GPU accelerated effects, provided all you do is scale, rotate and translate (or skew, if that’s your bag).
I call them chrome, sorry google.