Those two are the only ones in the mansion who eats the core and seeds in apples, they eat the whole thing. They are also the only ones to like Green Apples. Sully doesn't though, so whenever Liu asks, 'wtf, why did i do that?' (Since he never notices) Sully replies saying 'ye'r a horse Liu' or 'horse instincts'.
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Liu picked up on it and started doing it to Jeff whenever that happens.
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They both eat them while not thinking at all, so they dont notice until the apple is gone.
