Facial Scruff: One of BMO's morning duties is to pluck out any hair that grows on Finn's face so he can be "young forever." When Finn wakes up, he comments that his lip hurts again.
Fingore: BMO challenges the rat to a thumb war. The rat does what it would naturally do in such a situation: bite BMO's thumb.
Minor Injury Overreaction: BMO screams in pain and calls for Finn after the rat bites his thumb. Considering his thumb doesn't even move when it gets bit, it's likely that BMO was simply doing this for attention.
Sick Episode: Finn catches something after kissing BMO's rat-bitten finger. This carries over into the next short.
Tastes Like Feet: After Finn kisses the rat bite on BMO's thumb, he says "Tastes like rat."
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