Why is a cat shitting on my doormat

[JuniperNarni]

Gone out to be confronted by shit all over my doormat. I'm assuming a cat has done it. Why would a cat do this? This can't be normal behaviour can it?

Not very helpful but we had a fox which kept doing this over a few weeks (neighbour spotted it in action). We kept cleaning it up and it randomly stopped. Fox either moved on or died.

It's something to do with the texture. Our cat used to use the doormat if she couldn't get out for some reason.

Try rubbing orange or lemon peel on it or spray with peppermint oil. Should deter the cat.

Fox also occured to me after I typed this.
The mat was one of those bristly hard ones, it's been chucked because its beyond salvation and I just don't want to spend my morning trying to clean a unknown animals poo off a cheap doormat.

Thanks for the advise about lemon and peppermint, will this work as a deterent on just the step?

My concern is now that there is possibly a poorly cat somewhere and I should find out who owns it and inform them (there's only one cat that is a regular on our street). Or the cat/fox/unknown animal will come back every night and use my doorstep as a toilet.