Is laughter contagious?
Scientists now have evidence to suggest that, among our mischievous kea, it is.
Researchers reporting in the journal Current Biology have found that the particularly playful endemic parrot has a "play call" with a similarly powerful influence.
When other kea hear that call, it puts them into a playful mood.
The findings make kea the first known non-mammal to have such an "emotionally contagious" vocalisation, the researchers say.
Earlier studies had made similar findings for chimpanzees and rats.
"We were able to use a playback of these calls to show that it animates kea that were not playing to do so," said study co-author Raoul Schwing of the Messerli Research Institute in Austria.
"The fact that at least some of these birds started playing spontaneously when no other birds had been playing suggests that, similar to human laughter, it had an emotional effect on the birds that heard it, putting them in a playful state."
The researchers became interested in this particular call after carefully analysing the kea's full vocal repertoire.
It was clear to them that the play call was used in connection with the birds' play behaviour.
That made them curious to know how kea in the wild would respond to the recorded calls.
To find out, the researchers played recordings of play calls to groups of wild kea for five minutes.
They also played other kea calls and the calls of a South Island robin as controls.
When the birds heard the play calls, it led them to play more and play longer in comparison to the other sounds.
"Upon hearing the play call, many birds did not join in play that was already underway, but instead started playing with other non-playing birds, or in the case of solitary play, with an object or by performing aerial acrobatics," the researchers write.
"These instances suggest that kea weren't 'invited' to play, but this specific call induced playfulness, supporting the hypothesis that play vocalisations can act as a positive emotional contagion."
For the rest of us, the findings come as an intriguing reminder: "If animals can laugh," Schwing says, "we are not so different from them."
Scientist: Pluto's a planet
A US scientist wants to make one thing clear: Pluto is a planet.
So, says Johns Hopkins University scientist Kirby Runyon, is Europa, commonly known as a moon of Jupiter, and so is the Earth's moon, and so are more than 100 other celestial bodies in our solar system that are denied this status under the prevailing definition of "planet".
The definition approved by the International Astronomical Union in 2006 demoted Pluto to "non-planet", thus dropping the consensus number of planets in our solar system from nine to eight.
The change - a subject of much scientific debate at the time and since - made no sense, said Runyon, lead author of a new paper making the pro-Pluto argument.
Icy, rocky Pluto had been the smallest of the nine planets, its diameter under three-quarters that of the moon and nearly a fifth of Earth.
Still, Runyon said, Pluto "has everything going on on its surface that you associate with a planet - there's nothing non-planet about it."
Runyon, whose doctoral dissertation focuses on changing landscapes on the moon and Mars, led a group of six authors from five institutions in drafting a proposed new definition of "planet", and a justification for that definition.
The science of ... jokes
Can science explain why we find jokes funny?
A new study which drew on rats - and puns - suggests so.
Aiming to answer the question of what kind of formal theory is needed to model the cognitive representation of a joke, Canadian researchers suggest that a quantum theory approach may be a contender.
In the paper, they outline a quantum inspired model of humour, hoping that this new approach may succeed at a more nuanced modelling of the cognition of humour than previous attempts and lead to the development of a full-fledged, formal quantum theory model of humour.
This initial model was tested in a study where participants rated the funniness of verbal puns, as well as the funniness of variants of these jokes, such as the punchline on its own, or the set-up on its own.
The results indicated that apart from the delivery of information, something else was happening on a cognitive level that made the joke as a whole funny.
Because its deconstructed components didn't have the same effect, this led the scientists to believe a quantum approach was appropriate to study the phenomenon.
For decades, researchers from a range of different fields have tried to explain the phenomenon of humour and what happens on a cognitive level in the moment when we "get the joke."
Even within the field of psychology, the topic of humour had been studied using many different approaches.
Although the past two decades have seen an upswing of the application of quantum models to the study of psychological phenomena, this was the first time a quantum theory approach has been suggested as a way to better understand the complexity of humour.
Previous computational models of humour have suggested that the funny element of a joke may be explained by a word's ability to hold two different meanings - something called bisociation - and the existence of multiple, but incompatible, ways of interpreting a statement or situation.
During the build-up of the joke, we interpret the situation one way, and once the punchline comes, there is a shift in our understanding of the situation, which gives it a new meaning and creates the comical effect.
However, the authors argue that it is not the shift of meaning, but rather our ability to perceive both meanings simultaneously, that makes a pun funny.