The definition of cat got your tongue is:
(idiom) your silence is suspicious
Mom: Son, can we talk for a second.
Teenaged Son: Sure.
Mom: Are you hiding something from me?
Teenaged Son: No……why?
Mom: Do you know what I found under your bed?
Teenaged Son: No.
Mom: I found drugs under your bed!
Teenaged Son: ………
Mom: What’s wrong? Cat got your tongue?
Boyfriend: I had fun meeting your family last night.
Girlfriend: What do you think of my sister?
Boyfriend: She’s really nice.
Girlfriend: Do you think she’s pretty?
Girlfriend: Prettier than me?
Girlfriend: Cat got your tongue?
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