pick up on something phrasal verb ( see also ↑ pick )
1 . to notice something about the way someone is behaving or feeling, even though they are trying not to show it:
Children pick up on our worries and anxieties.
2 . to return to a point or an idea that has been mentioned and discuss it more:
I’d like to pick up on a point that Steven made earlier.
3 . pick somebody up on something to criticize someone slightly for something they have said:
I knew he was lying and I should have picked him up on it.