The chess lexicon has adopted a useful word from German, fingerfehler, fehler meaning mistake or error. Sometimes, the hand does not obey the brain. Imagine that you are busy contemplating A, followed by B and then C, and engrossed by the consequences of C. Meanwhile, the hand is eager to get involved, and picks up the piece to make move C. Standard competition rules are that once you’ve touched a piece, you must move it, so even if you catch yourself before executing the move, the damage from picking up a different piece may be terminal. Mercifully, I don’t recall ever doing this, but I’ve come close enough to know that the phenomenon is real. That’s my understanding of fingerfehler, although I’m just as often mildly frustrated to hear the word used interchangeably with ‘blunder’, sometimes by a player who would sooner blame their physiology than admit that their intended move was a straightforward howler.