It is a question that has baffled even the most accomplished horsemen and women for millennia: what’s in a snort?
Now, scientists in France claim to have come up with the answer - and it’s a happy one.
In a new trial, researchers moved 48 horses between comfortable, fun environments and enclosed spaces with little stimulation, measuring the frequency of snorts as they went.
They found the animals emitted significantly more of the explosive exhalations in favourable contexts.
Indeed, the correlation was so striking that the team at Universite de Rennes is now recommending equine owners listen out for snorts as a reliable indication of their horse’s state of mind.
Published in the journal PLOS One, the study clears up longstanding confusion among experts, many of whom have argued the snort signified nothing more than a hygiene response to unclean nostrils.
Meanwhile those who suspected it indicated an emotional were state split over whether this was positive or negative.
However, it was the similar noises made by rhinos while foraging which partly prompted the team to investigate the cause in horses.
The team evaluated snorts among 48 horses that lived either in restricted or naturalistic conditions.
These included riding school horses who spent much of their time in individual stalls and stable groups of horses always in pasture.
The researchers found that snorting was "significantly associated" with positive situations and with a positive internal state, as indicated by ears positioned forward or sideways.
For example, riding school horses produced twice as many snorts in pasture than when they were in stalls.
And horses living in naturalistic conditions - such as stabled horses who spent most of their time out at pasture - emitted significantly more snorts than riding school horses in comparable conditions.
Taken together, the researchers said their findings suggest that snorts are reliable indicators of positive emotions in horses.
They likened it to purring as a sound of contentment in other animals.
Previous research has indicated that horses have a complex ability to recognise each other’s individual neighs and match them to faces.
A study examined a group of 24 horses with the animals shown one of two familiar members of their herd who was led past them and out of sight behind a barrier.
After a 10 second delay, the horses were played a recorded whinny either from the herd-mate they had seen, or from the other animal.
When the sound did not match the herd-member seen walking behind the barrier, the horses seemed startled.
They responded more quickly and looked in the direction of the call for longer.
The research suggests that hearing the sound of a whinny conjures up visual memories of a horse's appearance.
Mathilde Stomp, who led the new study, said: "The snort, a non-vocal signal produced by the air expiration through the nostrils, is associated with more positive contexts - in pasture, while feeding - and states - with ears on forward position - in horses.
"Moreover, it is less frequent in horses showing an altered welfare."
She added: "These results provide a potential important tool as snorts appear as a possible reliable indicator of positive emotions which could help identify situations appreciated by horses."