I'd like to think I know the answer but this caused a huge rules argument and I want some other opinions.
If a player uses clairaudience on an npc who is communicating telepathically, does the player hear the telepathic conversation?
I said no, because to me telepathic communication is an exchange of thoughts, not sounds.
Another player said yes, because hearing something in your head would still use the same part of your brain that hears real sound. I have no real knowledge of anatomy, so I don't know if this is true.
I was the DM, so I just used the "what I say goes" rule, but I hate using that, especially when the players have a somewhat valid arguement.