Sheldon Finally Reveals Why He Knocks Three Times On The Big Bang Theory

Leonard and Penny must separate a quarreling Sheldon and Amy when their cohabitation does not go as planned, and Sheldon threatens to break off their relationship when Amy refuses to adhere to the bathroom schedule on the next episode of The Big Bang Theory entitled "The Hot Tub Contamination."

There's trouble in paradise for Amy and Sheldon!

1. There's trouble in paradise for Amy and Sheldon!

Sheldon and Amy's cohabitation experiment hits a roadblock and Sheldon threatens to break off their relationship when Amy refuses to adhere to his strict bathroom schedule. To stop the couple from quarreling—and keep their current living arrangement the same—Penny and Leonard separate ShAmy until everyone's cooled off. 

Meanwhile, Howard and Bernadette find unexpected guests in their backyard when they decide to stay home from a planned vacation on the latest episode of The Big Bang Theory entitled "The Hot Tub Contamination."

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Amy is irked when Sheldon brings up his issues with their living arrangement.

2. Amy is irked when Sheldon brings up his issues with their living arrangement.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Sheldon and Amy continue to bicker, which exhausts Penny.

3. Sheldon and Amy continue to bicker, which exhausts Penny.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Penny and Leonard are nervous that Sheldon will want to move back in with them.

4. Penny and Leonard are nervous that Sheldon will want to move back in with them.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Penny takes Sheldon out for ice cream so he can cool off and vent.

5. Penny takes Sheldon out for ice cream so he can cool off and vent.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Sheldon opens up about the real reasons behind his relationship concerns.

6. Sheldon opens up about the real reasons behind his relationship concerns.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Penny listens closely while Sheldon explains why he always knocks three times at the door.

7. Penny listens closely while Sheldon explains why he always knocks three times at the door.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Amy and Leonard stay back at the apartment while their significant others go out.

8. Amy and Leonard stay back at the apartment while their significant others go out.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Amy cracks a smile while discussing her romantic woes with Leonard.

9. Amy cracks a smile while discussing her romantic woes with Leonard.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)
Howard and Raj spend an afternoon at Stuart's comic-book store.

10. Howard and Raj spend an afternoon at Stuart's comic-book store.

"The Hot Tub Contamination" (Episode 5, Season 10 of The Big Bang Theory)