Quirky human behavior

In 1988, psychologist Fritz Strack of the University of Würzburg, Germany, asked two groups of people to judge how funny they found some cartoons. In one group, each person held a pencil between their teeth without it touching their lips, which forced a smile. The other group were asked to hold the pencil with their lips (not using their teeth), forcing a frown.

The results revealed that people experience the emotion associated with their expressions. Those with a forced smile felt happier, and found the cartoons funnier than those who were forced to frown...

Anthropologists and psychologists have long been interested in superstitions. One of the key categories of superstitious thinking is the "law of contagion", which says that when an object has been in contact with someone, it somehow acquires their "essence". Psychologist Paul Rozin and colleagues at the University of Pennsylvania have investigated how common such thinking is today.

They asked people to rate how they would feel about wearing a nice, soft, blue jumper that had been freshly laundered - but previously worn by someone else. As they varied the fictitious previous wearers of the jumper, it became clear how strongly people follow the age-old belief in magical contagion.

Perhaps unsurprisingly, the volunteers were unhappiest about wearing the jumper if they were told it had previously belonged to a serial killer. On the whole they would rather have worn a sweater that had been dropped in dog faeces and not washed - raising genuine health concerns - than a laundered sweater that had been worn by a mass murderer.

Even in the 21st century, we are far from being the rational creatures that we like to think we are, as a final part of the experiment made dismayingly clear. When asked to imagine that the laundered sweater had been worn by someone who had contracted HIV through a blood transfusion, most people once again said they wouldn't wear it.