My late dad was a nurse in a Victorian-era hospital with similar tunnels. These were accessed using ramps. Whilst training he was asked to move a deceased patient to the mortuary using the tunnels in the middle of the night.
As he went down one of those sloped ramps he noticed there was a leak. The way he noticed was finding himself on his backside and the trolley running out of control to hit a wall. The deceased patient rolled off the trolley and smacked off the wall and made a disturbing groan. My dad rushed over thinking the patient must still be alive, panicking the patient was now both not dead and possibly injured. Luckily for him but less luckily for the patient – the patient was still dead, but now had a laceration on the forehead. That’s the way my dad found out that dead bodies still make noises if air is pushed out of them.