The psychiatrist then returns, and attempts to diagnose the collective illness by asking indirect questions to each patient in turn ("Do you prefer the daytime or the nighttime?" rather than "Is your illness related to light?"). Patients can convey hints in their behavior as much as their answers.
If a patient gives an answer which is inconsistent with the agreed affliction, or is a lie, the other patients should shout "Psychiatrist!", and the answering patient swaps seats with the patient who shouted first. This game mechanic may be invoked voluntarily if the psychiatrist's questions are being too direct - for example, if the psychiatrist has worked out that the shared delusion is that of being a film star and asks one of the patients "What is your name?", that patient may choose to lie, knowing that another will then shout "Psychiatrist!
The questions do not have to be limited to yes/no questions, and generally tend to become more and more personal and risqué as the game progresses. If a player answers a question incorrectly, anyone who knows that the answer is incorrect shouts "Psychiatrist!" and everyone switches places. The true purpose of the game is to discover interesting and usually ribald information about the players, and also to discover how much people really know about each other.
Sometimes, the first time that the game is played in an evening, the Psychiatrist will not even be told that there is a pattern, and must deduce the nature of the game as well as the pattern. With a Psychiatrist who already knows how to play, the pattern tends to be quite esoteric ("the first person to your left who is a different gender but shares your hair color").