Research coming out of the Happiness Research Institute in Slough has discovered that smiling is almost as contagious as yawning.
"This has been our most fun experiment to date," said head Laughter Technician, Earnest Staid. "This has been more fun than the tickling experiment of 2003, when we wore tragedy masks to make sure it was the tickling that made people laugh, and not laughing ourselves. That turned out to be the masks that were making people laugh."
The latest batch of experiments has the scientists accosting random people in the street, and smiling at them.
"You would be amazed at the number of people who just can't help smiling back," said Staid. "Of course, a large percentage think that you are a lunatic. But if the smile looks genuine, the response you get is genuine. Or a punch in the face."
Staid has discovered that smiling is generally okay, but laughing at somebody usually elicits a less than friendly response.
"With a yawn," said Staid, "you can infect an entire bus load of people inside ten minutes, but a smile can infect only eighty percent and takes fifteen minutes."
Whilst only a handful of people with severe personality disorders are immune to yawning, it seems that at any one time, about a fifth of people are immune to smiling. Some people are permanently immune to smiling. Most of these are Scottish.
"Smiling has positive health benefits," said Staid, explaining why the Scots dislike it, "So spread a little healthiness next time you're on a bus, or in a crowded area. Put a happy smile on your face, and mean it. Spread the joy."