Sam crouches down next to the smear, frowning as he looks from it to the rug and back again. Then he stands, heading to the bathroom to get some water. Only about half a glass. Then he comes back, crouching again and judging some distance before pouring out a little water about six inches away from the smear, then continuing around in a circle.

It might have been there just from kicking the rug. But the rug might have been there to conceal something more.