It must taste good

While Megan is riding Daisy Sam is playing in the wagon.  He goes all over the wagon and every once in a while will climb out and onto my lap; but he prefers to crawl around and stand up on/in the wagon.  Today he was reaching down and touching the tires and getting the dirt/gravel/mud off of the tires again.  But today he would get it on his fingers and then stick them in his mouth.  I kept telling him to stop eating it but every time I would turn to watch Megan for more than a few seconds I would catch him trying to lick his fingers again.