Visual difference between Chest and Mimic

Just in case someone hadn't noticed, you can tell if a chest is a mimic by looking at it, you don't need to actually hit it (although that works just as well). Mimics actually have a lock on the chest, where real chests do not.

I didn't take a picture, but I believe it is the same for metal chests.

http://imgur.com/a/MWIiS