For the bridge convo, if someone leaves the bridge (to talk to the other) the convo stops.
To get around that I had one go half-way and the other eventually past the point that the ! appeared. When that happened I could make the talk, then get the poisoned character back and healed.
Not very fluid a sollution, but it worked. No achiev though.
According to a guide I read you should get it entering the Hunter's Edge map rather than the Phantom Forest. Doesn't make much sense to me, but could be possible. A friend of mine got it anyway... not sure how.
