The Infestation Hypothesis

Lore & Background

In the episode, Leonard and Priya continue their relationship via Skype, which annoys Sheldon. Sheldon visits Penny's apartment, sits in her new chair, and compliments it, but upon learning she found it on the street, he becomes paranoid about contracting "chair lice" due to his mysophobia. He unsuccessfully tries to get her to remove the chair and enlists Amy to talk to Penny about it. Penny is upset and accuses Sheldon of manipulating Amy; Amy apologizes and sits in the chair, where something bites her, causing both women to flee. Later, Howard and Raj find the chair outside and bring it to Sheldon and Leonard's apartment so Raj does not have to sit on the floor.

Meanwhile, Howard suggests Leonard and Priya engage in cybersex. During their next date, they begin to undress, but the screen freezes as Priya is about to remove her shirt. Howard later finds a pair of mechanical mouths that simulate kissing; Leonard is reluctant to use the device, especially after Howard and Raj demonstrate it. Later, Leonard begins to talk dirty to Priya before realizing her parents are listening.

Reader's Guide

The episode received mixed reviews. Oliver Sava of The A.V. Club gave it a C, noting it was "composed of two B-plots" and that it marked the first time someone explicitly connected Sheldon's behavior to a mental disorder when Amy comments on his knocking pattern. The TV Critic rated it 52 out of 100, praising the Priya and Leonard scenes despite the predictable plot, but finding the Sheldon phobia plot tedious. Jenna Busch of IGN rated it 8.5 out of 10, calling the Penny/Sheldon scene before the discovery "fantastic" and enjoying the developing relationship between Amy and Penny. Carla Day from TV Fanatic rated it 4.5 out of 5, describing Penny and Sheldon as the "best relationship on the show" and noting character growth for both Sheldon and Amy. The episode was watched by nearly 12 million viewers in the U.S. and was the most watched program that night.

Did You Know?

• The episode aired immediately after the season premiere, 'The Skank Reflex Analysis', and received 0.64 million more viewers than that premiere.
• In Canada, the episode was watched by 4.053 million viewers, making it the second most watched program that night.
• In Australia, a ratings error caused the episode's viewership to be averaged with a repeat, decreasing the reported figure from 1.606 million to 1.321 million.
• The episode featured a pair of mechanical mouths that simulate kissing, which Howard and Raj demonstrate to Leonard.