Okay,
the idea is that a topic is chosen and then each person posts one answer relating to that topic until we get 13. The person who posted the 13th answer chooses the next topic:

eg. 13 wizards

lauracullen: 1. harry

harrypotterfan: 2. ron

mrspotter: 3. dumbledore
... and so on until 13 then you choose another topic eg. 13 potions