Scientists who said in 2017 that sheep could recognize human faces from photos may be feeling a little sheepish right now, after experts questioned one of their conclusions.

Facial recognition specialists from Australia recently revisited the 2017 study. They admitted that the experiments provided "a compelling demonstration" that sheep could differentiate between human faces, but they challenged the authors' conclusion that sheep could recognize faces as well as humans and other primates can.

As experts in human facial recognition, the Australian researchers reported serious reservations about sheep performing this un-ewe-sual ability on equal footing with Homo sapiens. [The 12 Weirdest Animal Discoveries]

For the study in 2017, scientists trained eight sheep to recognize the faces of four human celebrities, including former president Barack Obama and actress Emma Watson. Then, they tasked the sheep with selecting the familiar celebrity faces when presented side-by-side with unfamiliar faces.

During the trials, the sheep selected the familiar faces 79 percent of the time, hinting that their choices were guided by recognition and were not random, Live Science previously reported.

The researchers also noted that sheep — like people — found it more challenging to choose correctly when a familiar subject had a different head position or hairstyle. Faced with these variations, the sheep's successful choices dropped to about 66 percent, and other studies have shown a similar decline in human facial recognition under those conditions.

Does that mean facial recognition in sheep is "comparable" to humans? Not exactly, the Australian scientists wrote in an article, which was published online Jan. 23 in the journal Royal Society Open Science.

In prior studies with human subjects, facial recognition tests were typically more rigorous than those that were performed by the sheep, involving more faces and less time to take the tests. Experiments that were referenced by the sheep researchers actually saw the human participants learning to recognize 24 faces, and they were asked to do so in a fraction of the time allotted to the sheep, the researchers reported.

Furthermore, extensive data on human-face recognition in humans indicates "that humans typically attain accuracy well above that achieved by sheep, on recognition memory tasks that are more complex and more demanding," according to the article.

Finally, describing facial recognition in sheep and humans as "comparable" would require data for humans and sheep performing equivalent tasks, the scientists wrote. Without that, it's difficult to perform any "meaningful comparison" between their abilities, according to the authors.

Originally published on Live Science.