He later decides to avenge the kis by giving her a Christmas gift. In Sheldon's logic, since she has not bought a gift for himself, he feels gesture would ruin her Christmas and make her sad.Sheldon, Amy, Leonard, Penny and others were out shopping for a Christmas tree, when Amy kises Sheldon in public, which makes him unhappy.Leonard and Wolowitz will spend Christmas Eve in the lab and get into a tiff after a potential disaster at the university. As a result, they will seek help from Raj, and which leads to the three friends scrambling to remove a pigeon from the clean room at the university.