rictus -- Jack

ric·tus (rkts) n. pl. rictus or ric·tus·es 1. The expanse of an open mouth, a bird's beak, or similar structure. 2. A gaping grimace: "his mouth gaping in a kind of rictus of startled alarm" (Richard Adams). [Latin, from past participle of ring, to gape.] rictal adj.

The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.

 

Jack is difficult to fool or to startle, so you'll seldom see on him the rictus of shock.