The Hot Tub Contamination is the 5th episode of the 10th season of The Big Bang Theory.
Howard and Bernadette discover that Raj and Stuart use their hot tub when they're not around. Meanwhile, Leonard and Penny are forced to get involved when things don't go smoothly with Amy moving in with Sheldon.
- Big "WHAT?!": Howard exclaims "What?!" when he learns that Stuart uses the Wolowitzes' hot tub when they're not around.
- Brick Joke: The raccoon.I told you raccoons don't say "Uh-oh."
- Hammerspace Hideaway: Where Stuart must have been while under water, given that Raj gets in the pool and appears to stretch out a bit yet never notices him there. It's not that big a hot tub.
- Naked People Are Funny: Stuart confesses that he is not wearing anything as he sits in the hot tub.
- Offscreen Breakup: Raj confesses to Stuart that he's single, meaning he broke up with Emily sometime after her last appearance. He says it was by choice, though not his choice.
- Pants-Free: It's only at the end that Stuart confesses that he was naked in the hot tub the whole time.
- Primal Scene: Sheldon reveals that he once walked in on his father having sex with another woman. It's also the reason why he always knocks three times; the first knock is traditional, the other two are to give them time to put their pants on.