I just realized...
"Jester:
I've got it! I've got it!
The pellet with the poison's
in the vessel with the pestle.
The chalice from the palace
has the brew that is true. Right?
Greselda:
Right! But there's been a change...
They broke the chalice from the palace.
Jester:
They broke the chalice from the palace?
Greselda:
They've replaced it with a flagon.
With a figure of a dragon.
Jester:
A flagon with a dragon?
Greselda:
Right!
Jester:
Did you put the pellet with the poison
in the vessel with the pestle?
Greselda:
No! The pellet with the poison's
in the flagon with the dragon.
The vessel with the pestle
has the brew that is true."
Unless they emptied (and washed) the vessel with the pestle after they broke the chalice from the palace, BOTH CUPS WERE POISONED!!!
I've seen this movie many times and until just now, when I read the script lines, did I realize this.