Big smiles, everyone!
The three participated in an extra-special segment called "Mouthguard Talks," where they popped in dental mouthguards and attempted to have a regular conversation. They wore bibs to protect themselves from the spittle and drool they inevitably encountered while talking.
Corden, McCarthy and Schaal also tried to do "normal" things like drink water and blow bubbles, which sent them (and the audience!) into hysterics.
Just try to keep a straight face through this segment -- it's impossible.
We leave you with this: