Perhaps the look in his eyes was enough to tell her that she was right; he looked as trapped as any wild animal, and never mind that he also looked hungry, in a strange sort of way; her response was so sudden, his startlement so all-encompassing, that at least he wasn't completely embarrassing himself by becoming visibly erect.
"Oh," he half-gasped, half-squeaked, or perhaps there was no sound at all, and it was just his mouth falling open.