His dominoes get so dirty because he plays with them allllll the time. We usually will scrub them in the bath with some dish soap, but even then most of them are stained. That's how much he loves those stupid rectangular tiles.
On this one he combined his rube goldberg machine skills with his dominoes.
He's impressive. I'm so interested in what he will be when he grows up. If it's not something in engineering I will be surprised.