Ignore it as best you can
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What's the point of trying to copy it? It doesn't seem to need you.
A matter of luck: It could go either way (success chance: 50%)
It doesn't like being ignored. It turns and walks away. Hah. You won. Hah.
You were right
Your reflection doesn't seem to need you to return its smile. And its smile is so very unpleasant. It hints at sharp incisors and a reptilian tongue.