"We're looking for rocks! Do you have any rocks we can have?"
"What do you want the rocks for?"
"we've been gathering rocks so we can have a rock sale. We're going to split the money, with my share I'm buying an Ipad."
The second girl nudged the speaker at this, presumably for revealing their secret scheme.
I think for a moment, then find the bag of lava I picked up in Hawaii. I give them a small piece of aa lava.
They then wandered off, satisfied.
I hope they do as well as the "Pet Rock" guys did.