The most basic way to describe Willis face is to draw a O for Willis was not expecting Liz to slap her nor did he expect Cas to just blurt it out that he was the father, after all he had a reputation to uphold, what would his friends and colleagues think!? Cas was going to be a issue but he refocused on the event at hand "I... Abandon... I... No..??" Willis knew he was making a fool of himself and nothing he could say would fix it but somehow still managed to get a small "Sorry" out.