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Horses seem to recognise themselves in mirrors, and they may even use the information in their reflection to recognise if their face is dirty and needs wiping clean.

Eleven horses out of a group of 14 tried to rub coloured marks off their own cheeks after they discovered them in a mirror. This makes horses the only animals besides primates found to be generally capable of self-recognition in a mirror, says Paolo Baragli at the University of Pisa in Italy.

Self-recognition has previously been detected in a few other species, such as elephants, bottlenose dolphins, magpies and a small fish called a cleaner wrasse. But because there were only a few animals in each of those groups that showed self-recognition, scientists couldn鈥檛 say whether the species as a whole had the capacity, says Baragli. For horses, it does seem to be a general feature, he says.

Baragli and his colleagues put a large standing mirror in an indoor arena and let 14 horses loose, one at a time, in the open space. Initially, all the horses treated their reflection as though it were another horse. Some tried to play with the 鈥渙ther horse鈥�, and some were afraid or even aggressive towards it, says Baragli.

But after this initial reaction period, which varied considerably in its length depending on the individual animal, most horses changed their behaviour and began investigating 鈥� as though they wanted to 鈥渢est鈥� to see if the horse in the mirror was actually a reflection of themselves, says Baragli.

Eleven of the horses checked behind the mirror and watched their reflections as they moved their heads around. Some even stuck out their tongues at the reflection.

The researchers then used medical ultrasound gel to mark the 11 horses鈥� cheeks 鈥� which horses can鈥檛 see except in a reflection 鈥� with an 鈥淴鈥�. At first, they used transparent gel, but they later added colour to the gel to make it stand out against the horse鈥檚 skin.

When the X marks were coloured, the horses stood in front of the mirror rubbing their faces with their legs for five times longer than when the X marks were transparent. For Baragli, it is clear that the horses recognised from their reflection that they had something on their own faces, and they wanted to either investigate it or remove it.

But Gordon Gallup at the University at Albany in New York, the developer of the mirror self-recognition test, believes such conclusions are 鈥渄ubious鈥� at best. He disagrees that the horses were really investigating their mirror images as themselves to begin with. Having such 鈥渟elf-directed behaviour鈥� is a critical stepping stone in this kind of research.

鈥淣one of the horses spontaneously used the mirror to investigate parts of their bodies that could not be seen without a mirror,鈥� says Gallup. He says that without evidence of this self-directed behaviour, running a test in which parts of an animal鈥檚 body are marked and its reactions monitored 鈥渋s like putting the cart before the horse鈥�.

Baragli stands by his conclusions based on 22 hours鈥� worth of videos, which include multiple instances of horses looking at themselves, rubbing their faces and checking their faces in the mirror again. 鈥淭hey鈥檙e either trying to explore the mark on their face or trying to get it off,鈥� he says. 鈥淚t鈥檚 hard to imagine there鈥檚 any other reason for this behaviour.鈥�

Whether this would mean horses are self-aware 鈥� seeing themselves as individuals and conscious of their own uniqueness 鈥� remains to be determined. But self-recognition in a mirror is certainly an important 鈥渂uilding block鈥� of self-awareness, says Baragli.