Grows on Trees?

So our goodbyes with Grandpa Kay and Grandma Cheryl were tearful ones on Saturday at the airport. As they picked up their luggage, Kay slipped a $10 dollar bill into the hand of both Bryce and Zack. "That's for Sonic on the way home," he said. The boys were ecstatic. We hugged and kissed them goodbye and then pulled away from the airport. Robb then said something like, "Wow, grandpa must think that money grows on trees. Well, don't expect that anymore." Zack thought about it for a second and said, "Well, Grandpa will be back for my baptism in November so I guess money will grown on trees again in 2 months."