House peculiarity (2 of 2): Sandal crud.

After like 2 or 3 weeks in my new house, I noticed that there were these black pieces of crud that were appearing everywhere on the white tile, and I couldn't figure out where they were coming from, and then I started looking around and I ended up turning over my sandal and looking there and what do you know, there was like this mildly greasy black crud that had accumulated all up and down the sole of the sandal on each sandal. So, I washed them off, which left these kind of sodden wedges of like dustball and huge drops of blackened water in my bathroom sink, and that was that, although I couldn't figure out for the life of me where that crud came from, since it wasn't like my house sandals were outside or anything, and my house isn't that dirty, in fact it's rather clean and it's pretty easy to keep clean. Then, like a week later, I decide to turn my sandals over again, and there's some crud built up, not as much as the first time, but still, a noticeable amount! That got me checking more often, and now like every 3 days or so I wash the crud off of my sandals. As far as I can figure out, even though I regularly sweep the white tile that's everywhere in my house, there's something with this tile and these particular sandals that make the newly settled dust stick to the bottom of my sandals, and when I walk around, it must just accumulate and accumulate, even though there's not that much dust you can see on the white tile, even in the corners. It must be something with that particular rubber or the particular ceramic material of the white tiles or something, like something to do with static electricity, and science.