Tali does have a detachable head, so when there is no new missions yet, she decides to relax. But most times Jappy and Lobelia goof off with her "ability". Jappy snatches her head (or sometimes tosses it away) and uses it as a ball. Tali would have chased him most of the time, but Lobelia's hackbug or her charm makes her body either forget about being headless or even stop caring about her head for the moment (and THAT is what Lobelia and Jappy likes most. Such as glomping on her body, hugging, having fun etc.). That is Tali's disadvantage of having a detachable head.