Selective mutism defines one's inability to speak in certain situations. One who suffers this is actually fully capable of speech, but goes completely silent in one scenario, e.g. at school or in the presence of a violent family member or in Raj's case, when a woman is around. It is a serious anxiety disorder, usually paired with shyness and/or social anxiety.
The following points all have to be present for the disorder to be called selective mutism:
- The person consistently fails to speak in specific social situations despite speaking in other situations.
- The failure of speech lasts for over a month.
- The failure to speak is not due to a lack of knowledge of the spoken language.
- Communication disorders and psychotic disorders (which could explain the failure to speak) are absent.
In The Big Bang Theory
In "The Grasshopper Experiment", Penny discovers that Raj's mutism is nullified as soon as he takes a sip of alcohol. Unfortunately, he says very inappropriate things when he is drunk.
In "The Porkchop Indeterminacy", Raj enters a drug trial to suppress the mutism completely. It didn't work out.
Raj's shyness being the cause of his mutism is clearly shown in "The Griffin Equivalency", where he barges into Apartment 4A and starts to talk passionately, but he goes silent as soon as he sees Penny is in the apartment too. At the end of the episode, Raj wants to apologize to Penny by a letter, but Penny forces Raj to say it to her in person. For the first time in his life while sober, Raj actually says something to a woman he's not related to, and it only was a high-pitched "Sorry".
Raj drinks beer before hitting on Summer Glau in "The Terminator Decoupling". Leonard discovers it is non-alcoholic beer and concludes "some sort of Placebo-effect" is taking place. Howard, in jealousy shows it to Raj, who immediately goes silent. Apparently Raj only has to think he consumed alcohol to override his selective mutism.
In "The Wiggly Finger Catalyst", Howard finds another way for Raj to surpass his selective mutism: dating deaf girls. He introduces him to Emily, but the relationship fails because Emily only wanted Raj for his money.
When Raj finally gets a promising relationship with a girl named Lucy, they go on a date in the library in "The Contractual Obligation Implementation". Raj has promised himself to stay sober, so he surpasses his selective mutism by turning the date into a text-date.
After a quite harsh breakup with Lucy in "The Bon Voyage Reaction", he (again) isolates himself in his apartment. Penny comes to comfort him and he is able to talk to her. Penny simply assumes he is drunk again, but when Raj reveals he hasn't had a drink since last night, they're stunned. Raj has gotten over his selective mutism.
In "The Consummation Deviation", when Raj gets ready to have sex with Anu, his nervousness causes his mutism to relapse and he eventually admits it to her. Although she's upset Raj didn't tell her about it sooner, she's able to put it aside as she doesn't enjoy music and considers that to be her weird quirk along with Raj's mutism.