1
general::
see DOUBLE TAKE., Show a delayed reaction to an unusual remark or circumstance; also, look at something or someone again. For example, He did a double take when his ex-wife appeared at his wedding. [1930s]
American Heritage Idioms
2
general::
Phrase(s): do a double take
to react with surprise; to have to look twice to make sure that one really saw correctly. • When the boy led a goat into the park, everyone did a double take. • When the nurse saw that the man had six toes, she did a double take.
McGrawhill's American Idioms And Phrasal Verbs