WordNet
fall open
v. open involuntarily; "His mouth dropped open"; "Her jaw dropped" [syn: drop open]
Usage examples of "fall open".
She realized that at about the same time he did, and let her mouth fall open in a laugh.
Smith felt his jaw fall open as he saw the airplanes clearly for the first time.
She feigned sleep a bit longer, then let her legs fall open for him.
Ttomalss let his mouth fall open in a long laugh, which he thought well-earned.