During this episode, Penny and Sheldon are spending time together doing this test that claims it's possible to get two human beings to fall in love with each other very quickly. Of course, Penny does not take things seriously until Sheldon expresses his disappointment. She finally does and they have a nice time. Did they fall in love? No, but it did seem to make their bond a little stronger. During the Q and A part of the test, Penny learns this day is actually Sheldon's birthday. Nobody in the group knew up until now, including Amy, and Sheldon explains it is because "the thought of people jumping out and yelling 'Surprise!' fills me with more dread than the words 'George Lucas Director's Cut'." So, what does Penny do, she tells the gang it's his birthday and when he enters his apartment everyone jumps out yelling "Surprise!" After their lovely time together and he trusts Penny with personal information. So disrespectful and rude! Every episode that bothers me seems to always be because of Penny. She is just not a good friend.