Interesting idea and illo, but I don't think the executiuon of the card reader rewally punctuates the thought bubble it seems your comment below it is going for. I thought at first there was a calculator or a key card security clock on the stone, not a credit crad swipe. Maybe have a prince or the main character of the sword in the stone swiping the card?
Hahaha! Clever idea! I thought calculator at first as well, but then I got it when i saw the swipe part. Maybe you could add a little more to the swipe so we understand what it is: a pen for signing, some fairytale credit card company logos, or even some text that says "please swipe card". You could easily tweak this and resubmit it :)
About my design
In case you can, in fairytales would be card machine for paying!!!