On a related note (pun pun pun), I'm glad our insurance covers most of our appointments. Now I kinda want to look into why bill can mean what I have to pay someone and also paper money and also a
shortening of "William" which does not have the letter 'b' in it anywhere. I recall overhearing a group talking about how British or Medieval names change the first letter in the diminutive (i.e. Margaret to Peggy) and William would fit that.
Explanation of the comic is that Mark opened the mail and found a bill from our dentist. I thought he was meaning a $20 green note but he was in fact meaning we needed to pay $20 to our dentist since insurance or previous payments didn't quite cover everything. I mean, it would have been odd for our dentist to send cash to us so the payment request makes much more sense.
HAPPY SEPTEMBER! It's the most wonderful time of the year!
Text:
M: The dentist sent us a twenty dollar bill.
L: Yay!
M: No, not that kind.