During the talking head scene where Michael is explaining why he spent so much on magic items, you can see the fake thumb on his hand. It seems he was going to use the prop but it got cut from the final edit.
When Michael tells Jim "my lips are sealed" about keeping the secret, he sings the titular line from the song "My Lips Are Sealed" and says "Bangles." Michael wasn't correct--the song is actually done by The Go-Gos.
The trivia item below may give away important plot points.
Dwight catches Oscar faking being sick. So for Dwight to not tell Michael he says Oscar owes him a huge favor whenever he wants. Later in the series, Dwight holds a funeral at his farm and invites no one from the office except for Oscar. This is the big favor but Dwight doesn't actually say that it's the favor.