1) Gape 2) Gaping expression 3) Gaping grin 4) Opening of the mouth 1) Grin 
gaping mouth; orifice
• (n.) The gape of the mouth, as of birds; -- often resricted to the corners of the mouth.
Ric'tus noun [ Latin , the aperture of the mouth.] The gape of the mouth, as of birds; -- often resricted to the corners of the mouth. 
based of bill where the mandibles join. Gape.
[n] - a gaping grimace
noun a gaping grimace
Base of the bill where the mandibles join; gape, commissure.