"Powers tend to be useful," Ezra says "granted, not always ideally useful. If the power of killings is about killing living things... you could with a lot of train and practice use it to kill cancer cells. Now, puppy summoning, if you don't want to sell puppies and don't have a second power that makes the first one useful... You can trade your power away."

Ezra thinks for a moment.

"Exchange rate of puppy summoning sounds very low, but you could get a deal where you age normally but gets back to equivalent twenties every thirty or forty years. You can trade the killing power too for a better deal."

The sisters might notice that he manages to say "puppy summoning" twice with a completely serious face.