Grandpa and Grandma were living with their son and daughter-in-law. Grandpa noticed that his son had a bottle of Viagra and asked if he could have one.
His son said, "Dad, I don't think you should take one - they're very strong and expensive."
Grandpa said, "I know, but I want to try one. How much are they?"
His son replied, "£10 each."
Grandpa only had a £50 bill but was going to the bank. He told his son that he would leave £10 under his pillow that night.
The next morning his son found £110 under his pillow and said, "Dad, I told you it was only £10. There's £110 under my pillow!"
Grandpa said, "That's ok, the other £100 is from Grandma."