Marty catches the expression, the little laugh, but doesn't understand it. Did he embarrass him by asking? But then, he doesn't seem upset, and he does put it out, so maybe it was the right thing to ask. Showing concern for other people is so complicated.

"Up up and away!" he agrees, a playful grin returning to his face. "After you," he says, then gestures, gentlemanly. This is quickly revealed to be a ruse, however, because once Liam is halfway up, Marty uses it as a chance to smack Liam on the butt and say, "Hurry up, slow poke!"