Sheep playing on 'vertical' cliffside baffle viewers

A video shot by a scientist in China shows a flock of carefree bharal - or blue sheep - frolicking and grazing on what appears to be a sheer cliffside.

"Blue sheep doing the impossible, per usual, in the Valley of the Cats, China," conservation biologist Imogene Cancellare tweeted with the video.

The clip has been viewed 1.3 million times since it was posted on Thursday - and responders swiftly fell into argument about whether it was an optical illusion or not.

Some suspected Ms Cancellare had given her camera a cheeky tilt to make it seem the cliff was steeper than it actually was.

But others were inclined to believe no trickery had taken place, and that blue sheep were genuinely immune to gravity.

The debate, no doubt, will continue.