Time reference: 16th-ish century. Magic does not exist, and the story is well-grounded in real laws of physics.
I want to convince the king of my country that I'm a magician (for reasons unrelated to the question). However, magic does not exist, and I am a regular, meek person, and have to solve the problem using my own wits.
I have never met the king in person. I tried to make an appointment several times, but I was declined. The king really likes war and enjoys raiding neighbors. He is warlord-type of characters; sometimes consumes alcohol. He is not very gullible, so just saying "you know, I can do magic" won't help.
The king has just captured a small neighbor county. He led the army himself, and now he is returning home. He does not often have the opportunity to travel around his huge kingdom, so decided to stay for several days in a village that just happens to be very close to the route home. The village is known for its eccentric local cuisine and traditions, so of course, the king (along with several high-ranking officers) would try it himself. It is also located on the outskirts of the kingdom, so little of the factual information is available outside (i.e. there are rumors, and everyone in kingdom knows that "weird guys live here", but few have been here to tell exactly why).
The organizer that will prepare food for the dinner and organize the event is my friend that is ready to participate in my plan. I saw an opportunity here, and spend all my money and social "credits" and to convince/bribe my way to be on this dinner. This is my only chance.
So, now I have a few weeks before the event for preparation. Because my friend has conspired with me, and the rest of the organizers are bribed (but guests are not), I can fiddle with food and the dinner procedure as I wish without raising much suspicion. I can make the king drink strange beverages/dance/lick stones/do all sorts of random activities. This village is known for its unusual food and rituals, after all.
- I cannot do any permanent damage to the king. Otherwise, his officers will just pull out their swords, and I'll drop my head.
- Ideally, the effects should not seem to be related to the food. For example, if the king eats something, and his stomach starts aching, guests might think that something is wrong with the food. Then, we'll be immediately chopped to pieces.
What can I add to the food to perform a trick to make me seem like a person capable of magic?
Of course, I can pull out my handwavium that will, for example, make the person that eats it temporary colorblind. I'll add it to the dishes, and once it is eaten, I'll start discussing stained-glass windows. And, oh no, the king cannot make out the patterns. It must be a curse. Then, I'll "lift" the curse by taking the king to other room, sitting with him for an hour, and coming back. This would do, but I would like to have something grounded in reality.