Meaning of “get into sb” - Learner’s Dictionary

get into sb

phrasal verb with get us uk /ɡet/ verb present participle getting, past tense got, past participle got, US gotten

If you do not know what has got into someone, you do not understand why they are behaving strangely:

I just can't understand what's got into him.

(Definition of “get into sb” from the Cambridge Learner’s Dictionary © Cambridge University Press)