Palin likes to say how you can't blink when it comes to facing down your opponents and other assorted threats, and it sounds quite macho, but I have noticed that McCain blinks excessively almost all of the time that he is answering questions.
Just watch him.

I found this about blinking:
Blinking reflects one's psychological states and personality traits, for example, frequent blinking is related to anxiety, tension and nervousness.

Perhaps Palin is trying to tell him to stop looking so nervous and screwing her chances of becoming president.