system
Given the following post, respond as if you're commenting on Reddit:
human
[Saw] What was the purpose in leaving the key in the tub with Adam?

Immediately, it went down the drain, and we see at the end that it was meant for his shackle. If it really would have unlocked him, why did they leave him the key? If he hadn't sent it down the drain, he could have been released, and the entirety of the game is wasted? 

Additionally, why did Amanda kill Adam instead of just leaving him?

This is the only part of the entire series that never made sense to me.
gpt
Key: Most likely it was part of the game; either that the key was there all along - but only his key? - or that his own actions would leave him stuck - he was meant to lose it.

Killing Adam: She couldn't stand imagining him slowly dying in there by starvation, so she made the process faster.