The latest episode of Young Sheldon finally solved a mystery from The Big Bang Theory, seven and a half years later.
For those who don’t know, Young Sheldon is a prequel series to The Big Bang Theory and it follows the younger years of Jim Parsons‘ character Sheldon Cooper.
In the season 10 episode of The Big Bang Theory titled “The Hot Tub Contamination,” Sheldon explained why he always knocks three times before he enters a room.
He told Penny, “I was 13 years old, and on spring break from college. My mother was in bible study, I walked in the house expecting to find it empty, and I heard a sound coming from my parents’ bedroom.
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