Crocodile tears

With this curious locution, it is used to express a post-factum useless resentment: just like a crocodile, that tears up after eating, regretting a meal just taken. The same is when someone is saying to be sorry after doing foolishness without having the possibility to turn back and is dimmed to useless repentance. The origin of this expression is not certain: it could result from misunderstood acts of crocodile eyes that tear up (even if not necessary after taking the meal). The lachrymation is useful to these animals to clean up their eyes and it is physiological: the fact that it increases while it is out of water for a longer period (that coincide with the time of the stack on a prey) could have originated the misunderstanding.