Yeah, Season 1, Episode 20: https://subslikescript.com/series/Community-1439629/season-1/episode-20-The_Science_of_Illusion

That's okay. That's what I love about the show. It's fun to just watch, but there's a lot of extra content in the details. I've watched every episode several times, at least once with headphones, subtitles and my full attention, and there's no way I can remember every single reference. As long as you don't forget Troy and Abed in the Morning, you're good.