"What is normal?" Professor Adnam ran her gaze across the class - or those members of it who had bothered to turn up for the morning's lecture. The tiered seats of the hall were not even half-full, and the majority of those students in attendance had the appearance of only being physically present.

"Normal is originally a mathematical term," the professor continued after a pause. "However, in psychology we are more interested in it as a statistical term." She drew a sweeping arc on the blackboard in front of her, then tapped on it to try and attract the class's attention. "It relates more to the normal distribution of a set of statistical data. Like this. Anything that conforms to this is said to be normal. Of course, the term has now all but lost its technical meaning."

As she spoke, Professor Adnam glanced towards the emergency exit. A pair of eyes were visible through the glass of the door. The professor acknowledged them, then stepped away from the lectern. "These days, normal has come to mean something that is usual. Or worse, it has come to mean something that is correct." Behind her, a troupe of colourfully dressed and masked people filed into the lecture hall. A few of the students noticed them and nudged the people sitting next to them. "Today we shall focus on what normal means as a social construct, and how we must be careful of allowing our perceptions of normal to influence our observations."

The group behind Adnam started to move, going through a series of strange routines. Some danced and gestured at the students. Others ignored their audience completely and embarked on pantomimes of tragedy and slapstick. Every so often - at seemingly random intervals - the actors would change what they were doing. However, throughout this bizarre performance, the professor kept up with her lecture as if nothing was going on. The students, on the other hand, were fascinated by the events unfolding before them. They pointed and laughed; a few even applauded the antics taking place.

The performance did not last long. After a few minutes the actors stopped, formed a line and bowed to the students before walking stiffly out of the hall. Professor Adnam finished her lecture, then returned to her place at the lectern. She smiled at the students. "I trust that you have been paying attention." As she looked around the lecture hall, the professor noted that everyone's attention was now focussed on her. "I will be asking questions later."