to pick someone's brain
to ask someone for advice or ideas
brain drain
emigration of highly trained or qualified people from a particular country or organisation
to put two and two together
to reach a conclusion based on what you've seen or heard
to be out of your depth
to be in a situation that is too difficult to cope with
...wasn't born yesterday
not stupid or easy to deceived
to pull the wool over someone's eyes
to trick or deceive someone; to hide the truth
to be on the ball
to be very alert and aware of what is going on; very organised