Sometime before the events of "Little Gift Shop of Horrors," Stan somehow obtained or made the drug with the specific intent to knock out anybody who drank it, saving it just in case a situation that would require it would happen.
Near the episode's end, Stan, who is upset that the traveler hasn't decided to buy anything, offers him a "free sample" in the form of the potion. The traveler accepts and drinks it, then experiences a sudden sense of vertigo before falling unconscious. Its sleeping effect lasts only a limited amount of time, as the traveler wakes up to find himself encased in a glass box.
- 206. "Little Gift Shop of Horrors"