Poisonous Plants and the Undead
The living, when ingesting poisons, will become sick and possibly die. But when you are already dead, the shift in energies remaps how many substances will affect you.
Please note: The following is obviously not advice for the living.
Hemlock is often used as a “breath” freshener. Undead creatures do not, by nature, have working lungs, but they still communicate with voices. A few springs of hemlock polishes their eldritch odors into a light, fresh smell.
Undead creatures lacking a body (ghosts especially) are often presented with springs of oleander upon entering a party. It helps them achieve a physical form solid enough to enjoy the festivities as easily as their normally corporeal fellows.
White snakeroot makes for a great table seasoning. Zombies and other corporeal undead are often unshackled by the need to eat, but retained social customs and simple enjoyment often brings them together to break black bread. Salt, a dangerous substance for the undead and fey, is not welcome. Snakeroot petals, dried and very finely chopped, are used in its place.