Grandpa & Grandma were visiting their kids overnight.  Grandpa went into the bathroom & found a bottle of Viagra in the medicine cabinet.  He asked his son if he could take one.  The son said he didn't think it would be a good idea as they were very strong & also expensive.  

"How expensive?" asked Grandpa.

"Well they cost $10 each."

"Tell you what..I still want to try one & I'll leave $10 under your pillow as soon as I break this fifty."

The next morning the son wakes up & finds $110 under his pillow.

The son says "I told you they were $10...not $110."

"Well, it's $10 from me...the rest is from Grandma!"