It was an instant karmic event.
J2 found a stick of gum on the sidewalk, and convinced his brother, J1, that it was from the hotel room and got him to eat it. Then, once it was in his mouth, J2 yelled "ewww, you're eating sidewalk gum!!!!!", turned around to run, and ran smack into the corner of a square stucco (hence the complimentary scrap marks) column.
I keep trying to tell them about universal law, someday they'll believe me.