I had exactly the same situation happen to me years ago. I realised that the preferred trap was out of toilet roll, so moved to the middle of the 3 traps.
As I was cleaning up, I heard somebody enter the trap I had declined to use, and unload. Just as I was finishing up, they realised what they had done, and I heard a meek voice say “hello is anybody there, can you pass me some toilet roll?”.
I recognised his voice, but I believe that it is a human right to keep your identity secret from the person in the next trap, so I just legged it.