This is a defensive response but this same open jaw posture is also his hunting posture. Peter explained that the worm-like appendage near the end of this tongue, technically called a 'vermiform', functions as a lure. The turtle, who can stay submerged for three hours, holds his mouth open while at rest and the vermiform moves in the water acting as a lure to attract fish. Snap!
Next post, a beautiful raptor with liquid eyes and a few other things that warmed my heart.
Cumberland Gap National Historical Park
Alligator Snapping Turtle--Wiki
Kentucky Reptile Zoo