The Cohabitation Formulation

The Cohabitation Formulation is the sixteenth episode of the fourth season of The Big Bang Theory. This episode first aired on February 17, 2011.

Summary
Priya is back and she decides to date Leonard again. Howard is forced by Bernadette to choose between her and his mother.

Extended Plot
Howard and Bernadette just had sexual intercourse. After that, Howard immediately prepares to leave, and Bernadette feels cheapened by this and asks him to consider living together. Howard arrives home and as usual, his overbearing mother, Mrs. Wolowitz annoys him with her rude comments, although this time, Howard snaps and leaves the house. Leonard opens the knocking door to find Howard, requesting to stay at their apartment. Sheldon comes out and commands Leonard to make tea as Howard is depressed, Sheldon then tries to comfort Howard, but Howard accidentally mentions that Priya is in town and is staying with Raj. Because Leonard and Priya had a "past", he dashed toward Raj's apartment, when he got there Priya and Leonard talked in private, although Raj clearly forbade it. The gang is at the Cheesecake Factory when Leonard and Priya announced that they will be seeing each other again, Bernadette told Howard to choose between her and his mother. Amy has heard the news from Sheldon and rushed to Penny's side to comfort her. Howard shows up at Bernadette's front door and explains that he chooses her and has moved out of his mother's house. The gang is having dinner, Leonard and Priya are acting all lovey-dovey and this annoys Raj. Penny joins in and talks to Priya, Amy points out that Priya is an amazing human. After having sexual intercourse, Howard asks her for all the requests his mother usually carries out. Bernadette suddenly realizes how dependent the two of them are upon each other, and Howard moves back into his mother's house. Amy decides to check up on Penny, when the two of them are talking Penny suddenly bursts into tears, Amy grasps this golden opportunity to examine her brain for data. Later, Penny comes into the apartment to have Thai food. Sheldon, who is alone except for Amy, who is video chatting with him, explains that Leonard and Priya went to Catalina for the weekend, Raj is at home, forbidding it, and Howard has been grounded by his mother for "running away". Amy tells Penny that thanks to her contribution, she was able to do research on what makes monkeys cry. When she learns that Penny is still upset, Amy tells Sheldon to make her tea.

Critics
"It's episodes like this which keep me hoping the show can improve and get better. The attempts at characterisation were small but solid. This wasn't the funniest episode you will see, nor was the Howard stuff adequately addressed but it was still encouraging." - The TV Critic's Review

Quotes
(Howard comes home from Bernadette 's place. He puts his keys in the door, when he hears his mother shouting.)

Mrs. Wolowitz: ''WHO'S THERE?! ARE YOU A SEX CRIMINAL?!''

Howard: Sex criminals don't have KEYS, MA!

(Howard goes inside.)

Mrs. Wolowitz: WHERE WERE YOU SO LATE?!

Howard: I WAS OUT WITH BERNADETTE!

Mrs. Wolowitz: ''I KNOW WHAT THAT MEANS. I WATCH DR. PHIL! I HOPE TO GOD YOU USED A CONDOM!''

Howard: I'M NOT HAVING THIS CONVERSATION WITH YOU, MA!

Mrs. Wolowitz: GOD FORBID YOU GET ONE OF THOSE "NEW FANCY" SEX DISEASES!

Howard: NOBODY HAS A DISEASE!

Mrs. Wolowitz: ''I HOPE NOT: I SHARE A TOILET WITH YOU! IS THAT WHAT YOU WANT, TO GIVE YOUR MOTHER HERPES?!''

Howard: ''THAT'S IT, I DON'T HAVE TO TAKE THIS! (Howard storms out of the house and is about to leave.) AND GOOD LUCK WITH YOUR EYEBROWS IN THE MORNING!''

(Howard starts going, until he checks his pocket and he realises he forgot something. He goes back inside to get it and his mother starts shouting again.)

Mrs. Wolowitz: ''WHO'S THERE?! ARE YOU A SEX CRIMINAL?!''

Howard: Still leaving! I forgot my CLARITIN!

(It is revealed that Bernadette has kicked Howard out of her place and he has come back home to his mother's place with all of his luggage. He is putting his key in the door when his mother starts ranting again.)

Mrs. Wolowitz: ''WHO'S THERE?! IS IT A SEX CRIMINAL?!''

Howard: Nobody wants to do that TO YOU, MA!

(Howard goes inside.)

Mrs. Wolowitz: WHERE WERE YOU?!

Howard: DIDN'T YOU READ MY EMAIL?!

Mrs. Wolowitz: ''YOU KNOW I CAN'T TURN ON THAT FERKAKTA COMPUTER! I LEFT YOU SOME BRISKET ON THE KITCHEN COUNTER!''

Howard: THANK YOU!

Mrs. Wolowitz: REMEMBER TO FLOSS AFTER, WE HAVE THE DENTIST IN THE MORNING!

Trivia

 * This is the second of four episodes to have a "Previously on The Big Bang Theory" review of past events. It summarizes "The Irish Pub Formulation" and is spoken by Johnny Galecki. It is the only one of the four that isn't a season premiere.
 * Howard and Mrs. Wolowitz agree that all of the CSIseries have their merits.
 * Sheldon describes himself as Howard's tertiary friend, with Leonard being his secondary and Raj being his primary friend.
 * In this episode, Sheldon shows surprising empathy. At the end of the episode, it is hinted that this is due to Amy's opinion on the subject.
 * In the episode "The Middle Earth Paradigm", Sheldon offered tea to Leonard when he is depressed. This is similar to his act of empathy in this episode, and if someone refuses, Sheldon says that it's not optional.
 * It is revealed that Howard's mother wears a wig and wears fake eyebrows and he has to help.
 * This is the first time Sheldon is seen wearing a pair of jeans.
 * It is revealed in this episode that Leonard's sister is 38 and married.
 * In this episode, Penny is revealed to have a heightened sense of smell, especially when it comes to pizza and Chinese food, similar to Sheldon's "Vulcan hearing" ("The Electric Can Opener Fluctuation").