Note the attitude that you get when you DO bring it to the manager. If they dismiss it casually or become defensive, red flag. If they are remorseful (sincerely), forgive and move on. As thejessjones well stated, it is not likely the manager that feeds (esp. if it is a larger facility) and s/he might not be aware of the incident. Tell manager and let them address the situation. If you soon find another string in your hay after a discussion, then you definitely have cause and the responsibility to be openly concerned and assertive.
Sure there's right and wrong but mostly there's just a whole lotta different.