[observation]

I'm rereading now and have spotted a third example: <spoiler alert>

Severian describes how Master Gurloes is an educated man and that he talks to other people/beings through something like a radio network at the top of the Tower.

It was phrased like this:

"He was the only one of our guild - Master Palaemon not excepted - who was unafraid of the energies there and the unseen mouths who spoke sometimes to human beings and sometimes to other mouths in other towers and keeps."