The Big Bang Theory Season 4 Episode 10 : The Alien Parasite Hypothesis
Amy becomes attracted to Penny's ex Zack, whom she meets in a bar on a night out with Penny and Bernadette. She later discusses her symptoms (elevated heart rate, clammy palms, dry mouth, and an involuntary "hoo") with Sheldon and comes to the reluctant conclusion that she is sexually aroused. It is also pointed out that Sheldon might be jealous. Penny tells Sheldon there is "something" he could do in this matter, however, as usual, he misunderstands her point and makes a number of phone calls until he finds the right Zack to set up a date for Amy.