The Alien Parasite Hypothesis

The Alien Parasite Hypothesis is the tenth episode of the fourth season of the Big Bang Theory.

Plot Summary
To be added

Expanded Plot
Amy begins to have feelings for Penny's ex Zack, whom she meets in a bar on a night out with Penny and Bernadette. Amy and Sheldon later discuss her symptoms (elevated heart rate, clammy palms, dry mouth, and an involuntary "hoo!") and come to the reluctant conclusion that she is horny. Penny tells Sheldon there is something he could do about that, so he tries to set up a date with Penny's ex. This proves fruitless as Amy finds Zack as dumb as Penny does. As Sheldon and Amy are leaving the bar, she grasps his hand. He asks her why she is doing this. She says it is an experiment. After a short interval, she lets go and says, "No, nothing. Never mind." Meanwhile, Howard and Raj quarrel over who is the better superhero and sidekick between them. They get Leonard to referee a wrestling match between them, but neither guy gets touched as they dance in circles for hours.

Trivia
To be added