Re: The Americans is Delightful.
What was most important about the poison was what the maid believed. She simply needed to believe that going to the authorities was hopeless. I don't assume that they told her the whole truth about the poison. That wouldn't make sense, if they did, anyway. Besides, Elizabeth and Phillip both agreed that the operation was highly risky. Being deceptive about the poison could easily have been one of the many risks that they took.
“A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP” — Leonard Nimoy (1931-2015)