"The Platonic Permutation" is the ninth episode of the ninth season of The Big Bang Theory. The 192nd episode overall, it first aired on CBS on November 19, 2015. The story follows the characters throughout Thanksgiving. The first storyline explores Sheldon and Amy's relationship as they meet-up, after being broken up. The next subplot follows Bernadette, Raj, Emily and Howard where they volunteer at a soup kitchen and the last follows Leonard and Penny after they have a minor conflict as Penny forgets Leonard's birthday. "The Platonic Permutation" features a guest appearance of South-African American entrepreneur and business magnate, Elon Musk as himself. Critics had mixed reviews of the episode. Critics praised Sheldon and Amy's storyline, but were critical of the other two subplots and of Musk's appearance. Plot With Sheldon Cooper (Jim Parsons) and Amy Farrah Fowler (Mayim Bialik) still broken up and all of his friends busy for Thanksgiving, Sheldon tries to give Amy tickets he bought them to Thanksgiving dinner at the aquarium, but Amy suggests they can still go as friends. Despite initial awkwardness, Amy honestly answers Sheldon's questions about her dating life, and each wants the other to be happy, falling back into their old friendship. Later, Amy tells Sheldon she is ready to be his girlfriend again. Sheldon declines, since getting over her was too difficult, but wishes to remain friends. Amy hides her hurt feelings. Bernadette Rostenkowski (Melissa Rauch), Raj Koothrappali (Kunal Nayyar) and Emily Sweeney (Laura Spencer) drag Howard Wolowitz (Simon Helberg) to a soup kitchen to volunteer for the day, after Howard lies about going there to avoid Sheldon. At the soup kitchen, Howard hates washing dishes, but is delighted to meet Elon Musk, the founder of SpaceX. They bond over space travel. Meanwhile, Leonard Hofstadter (Johnny Galecki) and Penny (Kaley Cuoco) prepare Thanksgiving dinner at home for the gang. When he realizes she does not know his birthday, he proceeds to list personal things he knows about her, but accidentally reveals knowing she hates the orange lingerie he bought her, which she only disclosed in her journal. To apologize for reading it without permission, Leonard dances in the lingerie, asking Penny to post an image on her social media as punishment. Penny refuses, but Howard, Raj, Bernadette, and Emily barge into the scene in his apartment. Production The story was completed by Jim Reynolds, Jeremy Howe, and Tara Hernandez whilst