Left-click with empty hands to clap. A real noise through the normal pipeline: a bright flash in your own colour, about a 7 m front, and the floor hears it.
It is the light you have when you cannot or will not speak — and the creatures treat a clapper exactly like a talker, so a clap next to one gets you hit.
Flash brightness doubled and down on the floors it rings with a proper tail. Your own clap sits in your head rather than wandering between your ears as you turn.
The tutorial now teaches it before the first door.
Your voice has three reaches
Whisper, speech and shout now light their own distances instead of sharing one curve — and since reach is also how far creatures hear you, the three are the same statement.
The game now recognises WHICH of the three you did. Ordinary talking was being measured by its loudest peak and read as half a shout — it heated the floor and lit like one. A normal speaking voice now counts as a normal speaking voice; it is visible in the mic calibration screen ("heard as:").
Rats
The floors have rats — alone or in packs, living in grates, pipes and wall gaps. They are scenery, not a new enemy: the bite is harmless, just a jolt of the camera.
They scatter from loud noises and from creatures, which makes them a living sensor — if the rats bolt out of a room, something made them.
Occasionally one shoves a vent grate open and bursts out. Yes, that is deliberate.
When the floor's rage climbs, whole packs stampede past you out of different passages.
They eat corpses, they swim in the flood, and photographing one gets them a bestiary entry.
The metro goes deeper
A lower tier. Stairs lead down into underground passages running under the line — and every branch down there ends in a side room with its own loot, money and bodies, never a blank dead end. Creatures wander down too.
Lamps and alert beacons on the walls, vaults and ceilings of the metro, the lab and the offices.
Dead ends are closed off with real grates you can see through.
Flooded floors have no lower tier.
Lab medical bays
The lab now generates medical rooms — beds along the walls, a control desk, a scanner in the middle, a cabinet with a CRT terminal you can pick up and throw — plus stray medical equipment scattered through ordinary rooms.