1.NounAn abrupt movement, used, for example, as a comical reaction to a surprising sight, in which someone casually sees something, briefly stops looking at it, realizes what it is, and snaps attention back to it with an expression of surprise or disbelief.
"Smith passes the car and does a double take as he realizes it is on fire.; I swear I did a double take when I spotted that $100 bill lying in the gutter!"