A poor merchant dropped in the village inn to spend the night. He left aside his merchandise and asked the innkeeper to prepare dinner. The merchant had a few items and a couple of coins, but the greedy innkeeper thought:

Innkeeper: “Why shouldn't I take all his merchandise and money.”

While she cooked dinner in the kitchen, that thought never got out of her head. Finally she said to her husband.:

Innkeeper: “There is a merchant staying overnight in our inn. It would be good to take his merchandise.”
Husband: “There's nothing easier than that. Just put some of the herb named ‘mega' in his meal. Everyone who eats from the herb forgets something. And what would a merchant forget if not his merchandise?”

And that's what the innkeeper did. She put the herb in the merchants dinner. He ate the meal, thanked the innkeeper and went to bed. The merchant left the inn early the following morning. When the innkeeper woke up, she went to the merchants room immediately. But the room was empty.

Innkeeper: “Oh, you fool” – she started to scream at her husband. – “What foolishness have you told me about this herb. The merchant forgot nothing.”
Husband: “Then he must have forgotten something else!” – calmly said the husband.
Innkeeper: “He forgot nothing!” – shouted the innkeeper.
Husband: “It can't be! Think about it!”

The innkeeper started thinking: what could have the merchant forgot. Suddenly she slapped herself on the forehead and said:

Innkeeper: “He forgot to pay, you old fool!”