Bro becomes asphyxiated by the toxicity of your knock-out-poison.
Bro yells 'Help! PoisonerThief is trying to poison me!'

"Bro" was in my party and reported nothing in his affects list, and was taking no damage, etc. What exactly is this edge supposed to do? Whatever it is, it doesn't seem to be doing it. Thanks!

I'm not sure how one could see the echo and not end up with the affect, however said affect does show up as knock-out poison and not something more particular.

So I'm inclined to say it's working. A log from the victim's perspective would be helpful, though.