Sheldon and Leonard broke into Penny's apartment last night to clean it in order to alleviate Sheldon's insomnia. Leonard's not happy and uses sarcasm with Sheldon, who doesn't detect it well. When Penny confronts them about their actions, she uses sarcasm, and Leonard helps Sheldon identify her use of sarcasm. This clip can be used to facilitate discussion regarding how authors use sarcasm in literature.
Sheldon is in the car with his dad talking about his brother, and Sheldon says his brother is an acquired taste. Sheldon's dad mentions putting his brother in milk, and Sheldon asks if it's sarcasm. He indicates the clue that led him to believe it's sarcasm is: "you don't normally put people in bowls of milk."