Apple cores are the center part of apples. They are the part where the flesh grows from and connect to the branch of an apple tree.
It is the part that us as humans tend to throw away when the flesh has been eaten. It is also the part that contains the seeds which we are also not too keen on.
So can rabbits eat apple cores?
Unfortunately they can’t as the apple seeds are poisonous to them.
Apple seeds contain amygdalin, which is converted into cyanide when the seeds are chewed or crushed.
Cyanide is highly poisonous and can be deadly in high doses. (source)
Stick to giving them a little of the flesh, but nothing else.