This is a rather geeky question, but I work with 3D graphics and so it's been nagging at me:
Are the character contours made by duplicating the character geometry, sizing it up slightly (along the normals) and flipping the normals of the contour geometry (and changing the material for the contour geometry, naturally)? It sort of looks that way on some characters, like Strong Sad's chin; where the contour geometry for his head would (if my theory is indeed correct) intersect with the geometry of his ample belly.
I would be very pleased if someone on the team could satiate my rampant curiosity. :D
Also, I have enjoyed the first two episodes very much, just as I have enjoyed Sam & Max. Please continue entertaining us, Miss Telltale Games.
EDIT: I suppose an outline rendered via a shader intersecting with geometry would give a similar appearance. How will I sleep at night, not knowing?!