In the TV show beginning in 2012, Raphael does this at least once, when one of Leatherhead's booby traps flies at his head. [![enter image description here][1]][1] Michelangelo also retracts completely into his shell at least once. [![enter image description here][2]][2] And pulls only his head into his shell at least once: [![enter image description here][3]][3] In the 1990 movie, Michelangelo does it twice, the others do it once. In the comics, I think they all do it once, but I could be wrong. And as Richard notes, they all do it in the recent reboot. For example, Leonardo: [![enter image description here][4]][4] [1]: https://i.sstatic.net/3BCsx.gif [2]: https://i.sstatic.net/xQHBW.gif [3]: https://i.sstatic.net/A4672.gif [4]: https://i.sstatic.net/wUSKs.gif