Secrets of the ages

My father puzzled endlessly how it is that garden hoses tie themselves into knots, and was delighted to find an explanation in the subtle expansion and contraction that comes with heating and cooling. I puzzle endlessly as to how my shower mat acquires brown grunge around its little suckers when I always hang it up to dry immediately after a shower. In those five or ten minutes, does enough water accumulate around the suckers to create mineral deposits? I clean them with an old toothbrush, which works but is time-consuming and annoying.
( Wednesday meme )