Frog tongue mechanism has been well-documented, but only recently have scientists started looking at the remarkable combo of tongue softness and frog spit's chemical makeup.
For the frog, the mix of a super soft tongue and non-newtonian spit is why their prey sticks so well. The tongue pushes against the saliva as it hits its prey, applying a shear force to the liquid as it spreads. This makes the saliva runny, pouring into every bump and crevice of the frog's prey. But as the pressure drops, the saliva returns to a thick, gooey and elastic state, helping it grip onto the prey hard enough to withstand the crazy g-forces of being launched into the frog's mouth.
• The Secret to the Stickiness of Frog Spit (YouTube / Sciencium)