The Sumo Wrestler!!!!

Ok, so some of you do not know my boys. As of three months ago, they are 12 3/4 yrs old weighing in at 62 1/2 lbs and 9 1/4 yrs weighing in at 50 1/2 lbs. I was on the computer yesterday and heard this really loud THUMP! I ran down stairs yelling,"what fell?" As I am running down the stairs I see the older one sticks his face around the stairs and runs away yelling,"Mom's coming down!" I'm now thinking not only did something fall- but it must have broken too.
I find both children in the kitchen pretending like they have been studiously doing Homework- no one is fooled.
"What was that loud thump? " I asked loudly.
"Nothing" my oldest replies. The youngest is giggling quitely.
"No, there was a loud thump and I need to make sure everything is ok"
"Nothing fell, nothing broke" he continues with a big smile. His Mother distrusts this smile.
"What made that noise then?"
"I did"
"You did?" Remember even with his recent growth he may be 65 lbs soaking wet!" How?"
"I was Sumo wrestling!"He says proudly and demonstrates the biggest thumping step I have ever heard short of elephant steps.
"Whom were you wrestling?" I pursue with fear in my voice.
"No one, Bro was being a scared little kitten."
OK, are you laughing yet? When I tried to tell my hubby- it took 3 or 4 tries to get to the words Sumo Wrestling I was laughing so hard! How can someone so light make such a loud thump?
Figured you might need a smile today- this is the one my child gave me for my 18th anniversary- enjoy!