House had tested Wendy for strep throat at Terri's insistence and told her it was negative, just as he expected it to be. He tried to get away but Terri tried to get him to convince Wendy not to want an ice cream cake for her birthday. House noted Terri was very slim and Wendy was somewhat heavier and figured Terri was more concerned about her own image than Wendy's health.
He decided to tell Wendy that ice cream was far worse than it actually was. When Terri became flustered, House hit her with both barrels and intimated what she wanted was a prettier daughter so people would say she looked just like her daughter. He then told Terri to buy Wendy the cake she wanted.