[SPOILER] Plot Discussion Thread *Spoiler Alert*

[Paddy™]

Is the Machine's voice already distorted/tinny in that conversation? If I recall correctly, the Engineer was still an alternate personality of Mandus at that point. In other words, Mandus is having the conversation with himself.

The voice isn't tinny in this instance, so it's not a phone call. You can find the audio file here:

\Amnesia - A Machine For Pigs\redist\sounds\vo\09_sewer\vo_sewer_trigger_01_flashback.ogg

It's also worth noting that it's a flashback to a time when Mandus is clearly in his pre-amnesia mode, and before he had sabotaged the machine.

I'm not sure if we should take the fact that he has the same voice as the Professor into consideration.

It's not the professor, though. The game files label the speaker as "The Machine", and the professor wouldn't be answering Mandus' questions about his own facility. The professor also speaks in a much less sinister tone haha.

That Mandus is asking the Machine about the safety of having poop near the core, and the Machine's response that the poop is useful, says to me that Mandus isn't the one designing the machine or is at least in cahoots with someone who has more knowledge of the machine's design than he does.

It could mean that Mandus and the Machine are separate people, instead of two sides of the same crazy coin, or that it's just a little bit of a cock-up in the logic of the story.