The kidz today, with their music, likely presume mash-up to mean a song smooshed together, Glee! style.
It's also this; the mash-up ... of poo. I think perhaps it was maybe the fourth or fifth search theWife performed but finally find it she did; the coin theBoy swallowed a few days before after he'd been trusted, and how was theWife to know theBoy would eat the money?, with holding a two-dollar coin for a ride promised for his near future.
No, he did not get to go on the ride. We're not that soft!
As noted in a comment at the original post, theBoy was apparently excited to see the coin was tarnished and claimed therefore that his 'body ate the gold!'
And I say again. What a Chooky!
Anyway, big-ups to theWife for fossicking through fecal matter for a swallowed treasure to ensure it passed. It's not a task I envied.