Grandpa and Grandma were visiting the kids overnight, when Grandpa found a bottle of Viagra in his son's medicine cabinet.

He asked the son about using one of the pills.
The son said, "I don't think you should take one; they're very strong and very expensive". "How much?" asked Grandpa. "$10.00 a pill," answered the son. "I don't care," said Grandpa, "I'd still like to try one, and I'll
leave the money under your pillow as soon as I break this bill.

The next morning the son found $110.00 under his pillow. The son said, "I told you each pill was $10.00, not $110.00." "I know," said Grandpa. "The hundred is from Grandma!!!"