How do you show, not tell when a person poisons someone?

Question

How do you show, not tell when a person poisons someone? Instead of saying, "Robert put poison in his drink", what do you do to show that Robert did it? Do you just heavily suggest it was done by describing how the poison fluid spreads inside the cup of water? What are the things you can do?

Answer 1

Pick your Poison:

Poisoning would involve an action, or the action could take place prior, in which case you describe the effects of the poison and the reaction of the poisoner.

• Rupert poured the brandy into the tumblers, concealing his hands from the view of his victim. The signet ring on his finger pivoted open on the rim of the glass, and the powder within glistened in the amber fluid. He swirled the glass as the crystals vanished into the alcohol.
• John stabbed the the tiny needle into his wife's back. Just a prick, though. She jumped. "Sorry, hon. Did the spider bite you? I crushed it."
• Bob slipped on the nitrile gloves, and then took the vial from his pocket. A single drop on each finger would do the trick. The nicotine felt almost like grease. Bob ran his fingers across the door handle of the car. Bob could picture the car accident as his boss had an apparent heart attack on the drive home from work.
• Theodore sipped the wine again. His chest tightened and he began coughing. Julianne looked on blandly as he gasped and stared at her. "How...?" he attempted. "Oh, no." she said sarcastically. "Are you well? What, nothing? Ah, well. I always told you all that wine was bad for you." A smile peeked out of the corner of her mouth despite her best efforts.

Answer 2

Foreshadow it

Agatha Christie loves to leave books about exotic poisonous plants lying around. She also has medicines go missing, as well as drawing attention to a doctor's new prescription, or a nurse's punctual reminder. They are often red herrings, the actual cause of death is something else.

In Hitchcock's Suspicion, a mystery author brags the antagonist had pressured her to reveal her research into a common untraceable poison, but she resisted. He looks uncomfortable at the story.

Lampshade it

Swapping drinks with the victim, or insisting the victim have a drink – especially if the killer has used poison before.

Visual media may be able to indicate the poison is dangerous just by drawing attention to it.

The end of Suspicion follows the antagonist

ceremoniously carrying a glass of milk to his wife on a silver tray. We don't see if he has poisoned it, and the film ends before she takes it, but he is planning to kill her – if not this time, soon.