Neutrality

Here's a fun game. Ask a volunteer to stand neutrally in front of a crowd. Then ask the crowd which emotions they read in that person. If you're particularly nasty, ask them which emotion you have told the volunteer to convey to the audience.

Nobody will ever tell you "neutrality" or "nothing".

That is because it is simply impossible for humans to be neutral in their expression. Neutrality is an intellectual concept of the mind, not the absence of emotion.

This fits nicely into the idea that improv is not equivalent to writing on a clean sheet of paper, but to reading something that is already there, however elusive it may seem. When Michelangelo looked at a piece of marble, he saw the statue already in it. He read it.

So, read your partners on stage. Read the light, the music, the audience. Nothing is ever neutral. You can find inspiration in anything and everything.