When I read your post yesterday, I remembered seeing a reference somewhere that said the darker, non-sticky liquid was some sort of chocolate-liquid-based prop, allegedly so that if any of it actually got into an opening, as in under Moe's eyelids in 'Oily to Bed, Oily to Rise', it wouldn't cause serious problems. I meant to document that source when I first saw it, but forgot to do it. I haven't found it again yet, but will identify it when I do.
