Head
Something that doesn't require much thinking
off the top of my head
About someone who originated an idea
the brains behind sth
to not express emotions
to keep a straight face
to start thinking about something
come to mind
No idea any more
be at your wits' end
to argue
come head to head
to remember sth
rack your brain
to be put in bad light due to some actions
to lose face
have a sudden thought
cross your mind
to be aware/conscious
to keep your wits about you
to feel powerless
bang your head against a brick wall
to think very hard about sth
beat your brains out
to come to a difficult situation
to come face to face with
to express your opinion
give a piece of your mind
to make money by clever and/or dishonest means
to live by your wits
e.g. about fame or money, which make you feel better than everyone
go to sb's head
to ask a lot of questions out of curiosity
pick sb's brain
to make an effort
to put your mind to sth
to stop worrying about sth
to be a load off your mind