Pierce and Jeff sort of bonded while the former was stuck in the hospital. They're a bit like father and son. A very small bit.
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Yes, that's LeVar Burton. He's Troy's idol and he guest stars on the 2//11 episode of Community.
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Community Season 2 Episode 16 Quotes

Everytime I need to cheer up I just make fun of Pierce, but now it would just make me sadder. It's Gregory Hines all over again.

Troy

Pierce: It was the pills, they just took me over. I saw awful things: aliens, demons, Critters 3, and something called Bruce Willis Surrogates.