Taken aback -- nonplussed

from wordsmith.org

nonplus (non-PLUS, NON-plus)
verb tr. To put at a loss for what to do, think, or say; perplex.
noun A state of perplexity or bewilderment. [From Latin non plus (no more).]

"Until this encounter, my only knowledge of codes was the Navajo Code Talkers, the World War II Native American group who used their native language to nonplus the enemy."
-- Jane Greig; Higshmrk E Qcwxivc (No, That's Not A Typo); Austin American Statesman; Sep 14, 2003.

"Larger seeds, such as corn, peas, beans and squash, may be planted the usual way, then immediately covered with a loose hay mulch, 1 or 2inches thick. Covering the corn seeds nonpluses the crows."
-- Ruth Stout; The Couch I Live On; Organic Gardening (New York); July 17, 1996.