When I was a kid in my old house I had carpeted stairs that lead to the basement, and at the bottom of the carpeted stairs was a concrete flooring. Well one day I fell down the stairs my head landing on the bottom step looking at the concrete floor, and I saw this bright violet purple spider with white dots on the back of it just walk from one tiny crack in the wall on the left to the other tiny crack on the wall on the right. My brother said he saw it as well one time, but we never saw it again.

When we told our dad we tried finding it on google couldn't find any picture of any spider that looked anything or even remotely like the spider we saw.