Bark up the wrong tree

Context #1 Alex: I'm sure that Cynthia took my candy. Mike: Cynthia? There's no way she took it. Alex: I think she did! She was at school yesterday. Mike: So was everyone else! It's a big school. Alex: She likes candy. Mike: Lots of people like candy. I think you're barking up the wrong tree. Alex: Wait a minute. Why are you so sure she didn't take it?

Context #2

Young Aaron's birthday is coming up soon. He will turn five years old on his birthday. Aaron's parents have been keeping Aaron's birthday present as a surprise but Aaron really wants to know what his present will be. As a result, Aaron is asking his mother all kinds of unusual questions to try to discover what his gift is. Aaron asks if his mother or father have gone shopping anywhere different. Aaron asks if his present is larger than a loaf of bread. He asks if his gift is hidden in the house. Aaron asks many questions. Finally, Aaron's mother says...

"Young man, if you think that I will tell you what your present is, you are very mistaken. You are barking up the wrong tree!"

Meaning: To make a wrong assumption about someone or something.

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