Alice and Bob are in the same class in their prep school. Alice has recently moved chairs to be closer to Bob- and Dana has figured it out. While on break, Dana asks Alice, "You fancy Bob then?" "Yes you do!", Dana replies, then goes into the following popular ditty. (These days, many reverse two and three). Rather common with the Toy Ship, but can occur elsewhere. Basically, it's Dana figuring out that Alice/Bob exists before Bob figures it out. If it occurs with adults, the dialogue is usually more "explicit". Examples of Kissing in a Tree include: