时长:00:19:16 / 首播:2017-04-06
Sheldon pushes himself to work on his project with Amy and the guidance system with Howard and Leonard on the same day. He catches a cold and wakes up the next day, half-naked, with no memory of what he did since he took cold medicine. His notebook of classified information on the military project is gone. Tracking his phone, they realize Sheldon went to a Western-themed bar. He gets the notebook back but learns he told everyone there about the project, after making them pinky swear to secrecy. Meanwhile, Bernadette feels guilty about leaving the baby when she returns to work soon. Howard thinks she is mad at him but makes her feel better by saying they can change their choices if they want and Halley won't remember this anyway. Amy plays Soft Kitty for Sheldon in different languages using an autoharp.
Title reference: Sheldon losing his memory of the day.