So the reason I opted not to use lethal poison in this episode is an interesting one. In order to get Silent Assassin, the following conditions need to be fulfilled:
- The targets need to be eliminate and all objectives complete.
- Only the targets, no guards or civilian can be killed
- No bodies must ever be discovered
- No one can become suspicious of the player
- None of the player's kills can be witnessed
- If a camera spots the player, they must destroy the evidence tape.
But even within these objectives, there are some sub-parameters. For example, if the murder was a result of an "Accident Kill", then the body can still be discovered without failing the objective for "No Bodies Found". The idea isn't that there is no evidence of a murder, but rather that there is nothing linking 47 to the murder(s). Something that can be explained as a accident doesn't need to be covered up for that reason.
However, poison works somewhat differently. Unlike an accident, "Poison Kills" can only be explained away if no one is there to witness the poisoning. If a target dies of poison, and is found later, it won't fail the "No Bodies Found" condition. But if someone is with the target as they die of poisoning, then it does fail that objective. It also fails the "No Noticed Kills" condition.
So I opted not to use the lethal poison because there was a whole group of witnesses around Jordan Cross, which would have ruined my rating. Opting for emetic poison, which only isolates him, was the safer option.