The poison was in the ice cubes. First girl finished her drinks before the ice could melt enough to release the poison, and the second girl who nursed it allowed the ice to melt, releasing the poison, leading to her death
crapbaskets. maybe the girl who drank the 5 really quickly, her body wasn't able to metabolize the poison? and since the other girl drank slower, her body was able to metabolize it because it was given time to set in. I guess. idk.