Chickens will almost never eat any food that is bad for them.
This includes poisons as well as non-poisons snakes, frogs, song birds, grapes, lizards, scorpions, etc.
Be not disappointed, if a flock of chickens is unable to swallow its' food whole they are perfectly happy to peck it to pieces and swallow the food one morsel at a time.
I have even heard tails about free-range chickens eating an entire plow horse or mule if the farmer didn't pull the body far enough away from the barnyard.
And what ever you do..... NEVER NEVER fall asleep inside your chicken coop...... you may wake up inside your hens.