The heating in our building, of 100 yrs at least, gurgles and bubbles and sloshes unexpectedly. From that, two things:
The first is that it does not splash. It is restricted and it sounds restricted. A sound declares its provenance, and this is a thing for the observant to note. I note it, therefore. Water and air are mingling in a closed system composed of pipes, and that is all.
The second is that it makes our apartment for some reason feel like an ancient inter-stellar vessel. The kind that drifted off light-years ago, and on which time has been creeping, and has deformed the observed circle of Saturn in these last days as it returns full of changed human beings from the distant past, its pipes gurgling not unmusically.