Cow pats

I was going to say it will leave a grass stain because that's what cows eat. Notorious for being hard to remove. maybe dye the carpet green?
One of our dogs as a puppy, used to eat cowpat, and once was sick from it on a mat. But it was a very dark coloured mat so didn't show so much.

I think the carpet is doomed. I used a vanish carpet cleaner and put paper towel on top. There is a trail of about eight footsteps but oddly enough some people in this house didn't avoid treading on the the paper towel. It now seems well rubbed in and has turned bright green. Thanks for the advice. My mil was right. She took a piece of paper and threw coffee tea beer chocolate jam at it and rubbed it well in took the dried paper to john lewis and said I want that colour carpet. It was actually very nice russet tweedy mix. But I bet even she never thought of cowpoo.

I agree with phoenix. That system also worked when young cat (ie Purdy Puss) forgot to 'go' before she came in at night and got caught short. A piece of kitchen towel laid over the top and then let it dry and it is easy to get rid of. Trying to pick it up when fresh just means it gets rubbed into the carpet. My sense of smell is not very good by the way !!

That would avoid the risk of spreading it, or scrubbing it in, rather than out, iyswim

In some ways I would be tempted to let it dry, then stiff brush & then vacuum!