"Viagra" joke

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!"