when you capture an animal and feed it to another animal it is not nature. its just sadistic. if the snapping turtle happened to catch the rodent in the wild then its nature. putting the mouse in the small enclosure with the turtle is not nature.
if you fed the turtle by giving it a dead mouse that would be fine, but to put the mouse through undue pain and suffering is wrong. give it a quick clean death first. dont put it through the agony of drowning at the same time as being dismembered alive.
I'd be lying if I said I've never done that, but to keep them and play with them prior to feeding them to your turtle is a little far for me. I don't feed anything live to my turtle anymore, partly because I don't want a one eyed turtle.