Are you sure it's not poison?

DOCTOR: Have a seat. Your test results came back today.
PATIENT: Do I have an infectious disease, doctor?
DOCTOR: Well you're certainly showing many of the symptoms. But have you considered the possibility that it might be poison?
PATIENT: Poison? Why would you think it's poison?
DOCTOR: Excuse me. I dropped something. Ok, there, I picked it up. Hey, why don't you have a sip of that water.
PATIENT: Ok.
DOCTOR: Stop. Don't drink that, it's full of poison.
PATIENT: It's what?
DOCTOR: I just poisoned that water as I pretended to bend over to pick something off the ground, to show you how easy it would be for someone to poison you, even if they didn't know you very well, and even if they didn't have a good reason to do it.
PATIENT: You're my doctor, why would you threaten to poison me?
DOCTOR: Like I said, to warn you about poison, and because it makes me feel like God. Have you noticed your throat starting to close up?
PATIENT: Wh--
DOCTOR: I've been pumping poison gas into the room since we began talking. Don't worry, I have the antidote.
PATIENT: Give me--
DOCTOR: Wait. Are you sure it's not poison?
PATIENT: --Is it poison?
DOCTOR: Yes. Here's the real antidote.
PATIENT: ...
DOCTOR: Good. You're learning.

PATIENT begins foaming at the mouth.