cotton on
US /ˈkɑːt.ən ɑːn/
UK /ˈkɑːt.ən ɑːn/

1.
entender, perceber
to understand something after a period of not understanding it
:
•
It took him a while to cotton on to what I was saying.
Demorou um pouco para ele entender o que eu estava dizendo.
•
She finally cottoned on to the joke.
Ela finalmente entendeu a piada.