Okay, first of all, no one should poison anyone. But I think you missed the point Mr. Open post. They both poisoned the coffee. They thought they were gonna get the other and instead. The both got each other. Okay, that's simple.
only here to say those are tea cups, not coffee cups, and the color was of tea too - plus, the teapot is on the counter in the first scene all the coffee drinkers presume coffee, I think that's amusing
