How was It Done? Was It The Drink?
The viewer is led to believe that only one person can leave the Embryo Room alive. Did No.2 think that it might not be him, and if it wasn't, did he know how death was to be administered? Was it the drink, as the resuscitated No.2 demanded to know. And if it was, why didn't No.6 die because of the drink as well? And why the need to kill No.2 in the first place?
Well I don't think it was actually the drink that did for No.2, because as posed in the question, why didn't No.6 die because of the drink as well. So this fact leads me to believe that it wasn't actually the drink, but that No.2's glass was pre-laced with poison. And as to the question of how it was done, well apart from No.2 and No.6, there is only one other person in the Embryo Room at the time - the Butler! I have watched the surveillance film footage of 'once Upon A Time,' and No. 6 never went anywhere near that bottle, or No.2's glass. And even if he had, where would he have got the poison from? So the presumption is, like in many a good murder mystery, the
did it! Otherwise Monsieur Poirot, you tell me who did it, and why! Butler
Be seeing you