Scared cats question →[More:]Why would my cats be so freaked out by my neighbour's 3-legged cat?

A friend moved in over the road a few weeks ago. She has two cats, Stanley (sweet ginger boy) and Henry (black, sleek as a seal and with only 3 legs - right hind leg is missing following previous Henry v car contest where car nearly won).

Usually when another cat comes into 'their' yard, my girls'll either go out through the cat flap and see it off, or will face it off through the patio door.

But today, their first sight (I think) of 3-legged Henry, they were both obviously freaked and ran back and hid, peering out from behind the door at him.

It was quite funny to watch, Henry is a little thing and my girls more than outweigh him, the fat dollops. But why would they be scared of him? He's not aggressive and didn't seem to be 'staking his claim' to their yard by peeing in it. Could it be the 3 legs? NB: I have asked them and as usual they have not deigned to reply.