Age Potion

A couple received a letter from their daughter who went to study modern physics overseas, the letter read:

"My beloved Parents, I miss you so much and it breaks my heart to think that by the time I get back you'll be too old. So enclosed you'll find a bottle of potion I have invented. It will make you young, so when I return you'll be the same age as I left you.

NOTE: Please take only a drop"

So they opened the envelope and in it there is a bottle with a red potion. the man looked at the wife and says: "You go first." (typical of men!)

So the wife takes a drop thereafter, the husband follows. Indeed the wife turn five years younger. Years later the daughter returns home to find her mother young and pretty, carrying a baby on her back. The mother proceeds to tell her daughter how the potion worked and made her look young.

The daughter was delighted and asks after her dad.

MOTHER: Your father? Hmm, my child, your father was so jealous that I was so young and beautiful so he drank the whole bottle.

DAUGHTER: What? So where is he?

MOTHER: Hahaha, who do you think is the baby on my back?