put my finger on it

"I can't put my finger on it"

definition: We use this expression to say that we can't explain or fully understand something.

(nemůžu na to kápnout, nemůžu na to přijít)

example:
A: She looks different, doesn't she?
B: Yes, but I can't put my finger on it. Has she changed her hair?

A: Why don't you like Robert?
B: I don't know. I can't put my finger on it. I just feel we can't trust him.