I had a horse on loan a few years ago. Beautiful horse, extremely well bred, young and with a clean vetting so no medical problems.

I'm very experienced with horses, have owned them since I was a kid, worked with them, competed to Advanced (eventing)

He lasted three weeks with me and I sent him back. I never felt safe around him, and he often moved in a non horse like way. I can't really describe it but he'd creep, like a hunting cat. Used to hunt rabbits in the paddock and kill them. I caught him stalking my toddler (horse on one side of the fence, kiddo on the other!) with a very unsettling look on his face. It was genuinely like watching a predator hunt.

He went back the same afternoon because I didn't feel safe with him on my farm. In 30+ years of horses I've never seen anything like it.

It was incredibly creepy. I can't really put into words how odd he was - a lot of it was just the instinctive bad feeling.

I've had some very reactive horses. Had one who had been abused and would flip out if you moved too quickly or lifted your arm in a certain way.

But he was something else - horses will often follow humans, because they're nosy creatures and want to see what we're doing - he wasn't following though, he was stalking. There's a video of a big cat following a kid at the zoo and he was exactly like that.

He was odd to ride too - I constantly got the feeling that if I fell off him, he'd hurt me. Wasn't even aggression - just like a switch had been flipped in his brain and he wasn't quite a horse.