Trama

Amy discovers some unusual feelings and urges when she meets Penny's ex-boyfriend, Zack. Meanwhile, Howard and Raj argue over who would be a superhero and who would be their sidekick.

Amy experiences strange symptoms, which she believes are signs of a flu. They include an elevated heart rate, sweaty palms, dry mouth, and localized vascular throbbing. As Penny and Bernadette were present when the symptoms began, they know that Amy doesn't have the flu: she is in lust with Penny's ex-boyfriend, Zack Johnson. As Amy and Sheldon finally come to the conclusion that Amy is feeling womanly urges for the first time in her life, Sheldon has to come to terms with what his feelings for Amy are. They also have to decide how best to satisfy Amy's new biological urges. Meanwhile, Howard and Raj get into an argument: if they were to acquire super powers, who would be the superhero and who would be the sidekick. They have to come up with a way to settle the argument.—Huggo

While eating their take-out dinner around the coffee table, Sheldon complains that the next person who ate with their mouth full will be put to death. This comment is followed later by Sheldon asking what everyone thought the best number was. Not 5,318,008, as suggested by Raj, since upside-down on a calculator it spells "Boobies". Sheldon explains that the best number is 73 because 73 is the 21st prime number. Its mirror, 37, is the 12th and its mirror, 21, is the product of multiplying 7 and 3... and in binary 73 is a palindrome, 1001001, which backwards is 1001001.

Amy, Bernadette and Penny are spending their night out together at a bar. Bernadette loves the heart-shaped locket Howard gave her after yet another night of enduring his mother. Amy provides a factoid that the iconic Valentine's heart shape is not based on a human heart, but rather the shape of the buttocks of a female bending over. Penny's ex-boyfriend, Zack, stops by to drop off menus, and says "Hi". Actually, Amy let's out an involuntary "Hoo!" a couple of times, including when Zack bent over to pick up a box. Penny knows what is bothering Amy, but she misses that she is aroused.

Howard and Raj find out a lab tech got bitten by a rat that was injected with radioactive isotopes. They wonder which of them would be the better Rat-man and which could be his sidekick. Leonard is unhappy at still being at the nerds' table.

Amy is slicing up pieces of a human brain and having lunch with Sheldon. They try to analyze the symptoms she had the previous night. Raised temperature, sweaty palms, and vascular throbbing in her ears and genitalia. Sheldon reduces the causes to hyperthyroidism, premature menopause, an alien parasite, or sexual arousal. Amy eliminates hyperthyroidism & menopause. Amy and Sheldon must face the cold, harsh truth that she was sexually aroused by Penny's friend, Zack. Sheldon prefers the alien parasite hypothesis. To handle her condition, he suggests Star Trek and the teachings of the Vulcan way of Kolinahr. Amy wonders why she should use advice from some cheap science fiction show. Sheldon uses Kolinahr to suppress his anger at Amy and then leaves accidentally mistaking her brain slices for his lunch.

Howard wants the sidekick argument with Raj settled, so he puts a giant spider in a large jar and wants both of them to put one hand in the jar. First one to pull out his hand is destined to be the sidekick. Raj put his hand in and smiles because the spider was crawling up Howard's arm. Next they decide on a wrestling contest. Leonard is the judge as they spend the whole night circling and trash-talking each other.

Sheldon heads down to do laundry and runs into Penny. He starts to talk about this relationship with Amy which he thought was a purely intellectual one. She has changed and had become a slave to her baser urges...like Penny. Penny asks what the right scientific word was. Sheldon replies, "Forget science; she's horny." Penny tells Sheldon that he can help her with those urges. ("It's illegal to spay a human being!") Then he jumps to a conclusion and figures he might as well get it over with. Penny thinks Sheldon going to satisfy Amy himself, but he decides to get Zack to do it.

Zack meets them in the same bar and Amy approaches him saying, "I stand here before you, 130 pounds of raging estrogen, longing to grab your hold of your Gluteus Maximus and make Shakespeare's metaphorical Beast with Two Backs." Zack is confused as usual. ("My Gluteus what?") Based upon his ape-like expression, she decide to start using Vulcan disciplinary practice of Kolinahr for her urges, though there is one more "Hoo!" before she leaves. Outside the bar, she does try holding Sheldon's hand though she doesn't feel anything.

Title reference: One of Sheldon's theories about why Amy had her symptoms, which he thinks is more likely than her being sexually aroused.