Murphy lives in a world that is completly his own! He just seems to be clueless all the time. This expression does a good job of explaining it.
Robey has a completly different personality, best explained in this shot that mom got. Isn't this hillarious? He looks like mom just said "now make a funny face!"
Robey plays football! His owner (Fritz) plays the center and Robey's the quarterback. He catches the football and everything! Its so cool!