Q: As I remodel, I am finding droppings that are black for three quarters of the length with the rest being white. My building is pretty well closed off and I can’t figure out what is leaving this.

A: A snake or a lizard has been visiting. Both creatures have a cloaca, the final excretory chamber into which their intestines and urinary tracts empty before defecation. The white part of each dropping is uric acid which was deposited internally onto their fecal matter. It isn’t likely the reptiles will be a permanent problem. Your remodeling work will eventually close their entrances.