Surprise, take unawares. This term is often used in the passive, as in The United States was really caught napping the day the Japanese bombed Pearl Harbor. It originated in the mid-1500s as to be taken napping. Also see under off guard.
Dog Idioms Inspired By Our Best FriendsHot dog!, hot diggity dog is an expression of joy or surprise recorded as early as 1923. Where did other canine sayings get their start?
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.