The remnants of a good hard dump, when you haven't wiped properly, leaving a layer of ground-in faeces against your inner cheek and around your nipsy. after a while and the application of some sweat, gives off an odour that is unmistakeable and marks you out as requiring a re wipe!
Man 1 "Oh my life Humphrey are you cooking up some bumhole toffee, i can smell it from here!!"
Man 2 "Yes Tarquin, but it has turned to ass gravy
where i have been working so hard."