Are You Sure: or: Monothematic Delusion

Scene:  I am visiting Dad at the assisted living place.  He has dementia.  I have made out his Christmas cards.  All he has to do is print his name.  I give Dad a notebook to use as a firm surface to write on.

me:  Here ya' go Dad. 

Dad opens the notebook and begins to sort through it.
Dad: Oh, I know I have to do something with this but I forgot what.
Dad looks in an envelope.
Dad:  Oh, that's the doctor's bill.  I'm not paying it.  Not even five bucks.  I have to take care of Christmas.  Maybe the bank will give me a small business loan.

me:  Here's the first card Dad.  It's for your nephew and his wife.

Dad:  We sent one to my sister and her family.

me:  Your nephew is grown.  So he gets his own family card now.

Dad:  Oh.
Dad picks up the pen.
Dad:  This is a nice pen.
Dad: How should I sign this one?

We go through the same process for all seven cards. 
Forty five minutes later.

me:  We're all done!  You did good.
Dad:  What's those things you have on the envelopes?
me: Stamps.  They're stamps.
Dad:  They don't look like stamps.  Are you sure?
me:  I got them from the post office Dad.  They don't say how much the postage is is all.
Dad:  They look smaller than stamps.
me: Really Dad, they are stamps.
Dad shakes his head.

Dad:  We'll see if any of the mail comes back.

        Dementia.  Such a wonderful drug.