Underwater Beach Instrument

A jar filled with a strange liquid was sitting on my kitchen table.

"What's this?' I asked my son.

"An underwater beach instrument," he replied.

"Huh?'

"It works like this."  He picked up the jar and swished the liquid around.  Then he banged on the top like he was playing a bongo.

"Hey, that actually sounds pretty good," I said.  "What's in it?"

"Two flavors of Capri Sun juice pouches." He opened up the jar and took a swig.  "It tastes pretty good, too!"