Liz Buchanan BVSc MRCVS
Hello! This looks as though a mucousy layer has become incorporated into the faeces. My understanding is that this can occur with worms - for example, if they damage the gut lining cells and then a wormer comes past and they die and 'let go,' some lining cells may slough away with them. This effect can also be because of certain roughages / fibres in the diet (perhaps plant matter) or a possibly a slow speed of the faeces moving along the last part of the gut, or lots of superficial moisture being reabsorbed from it. It often isn't a problem as a one off. I am unable to identify a definite worm in this picture, although it isn't as sharp on my screen as it might be and there are one or two white areas on the left hand chunk of stool that I am wondering about.
In any case, if there are worms in there then the wormer has done its job, so the question may be accademic.