I don't leave them. I primarily feed live as I raise my own rats/mice. But when I do occasionally feed F/T I don't leave them either. I only have one snake I don't have to play the zombie dance with because she eats with absolute gusto. The rest you have until my arm cannot bear it anymore and you obviously aren't going to eat it even though your nose is riiiighht up against it. That feeders goes to the next snake. No waste here. They get hungry enough and they won't be so picky the next time.