This young Astros fan probably knew what would happen if he let his big sister "just hold" his newly caught foul ball — so he made sure to mark it as his own.
To turn that prized souvenir into a gross thing that she would never be able to confiscate, the little imp gave it a quick lick. Which, in that unwritten sibling court of law ruling, legally makes it his property.
Even the playful slap made it worthwhile.
Bonus. Since it fell on the ground, it probably still had that hot dog, peanut and Cracker Jack flavor too.