We know that mirrors can mislead by seeming to switch left-right symmetry but we do not expect it to change the shapes of things. But Mark Frauenfelder brings to my attention this fine illusion by Kokichi Sugihara that makes what looks like circles get reflected as squares and vice versa.
Can you figure out how this illusion works? The solution is given below the fold.
Here is someone who has figured it out and has produced a video explaining it.