In 2001, a team of British scientists concluded that sheep are able to recognize the individual faces of approximately 50 sheep and remember them for two years.
Keith Kendrick, a researcher from the Barbraham Institute in England involved in the study, measured responses from cells in parts of the sheep’s brain. The animals were shown mug shots of different sheep and an electrode measured activity in their brains.
"Sheep, like humans, have specialized areas in the brain for face recognition," Kendrick told National Geographic. He added sheep have a separate system, far less specific, for dealing with the recognition of other objects, such as rocks and trees.