How does Mr. Utterson's conversation with Dr. Jekyll increase the mystery over the relationship with Mr. Hyde?
From the chapter, "Dr. Jekyll was quite at Ease" in The Strange Case of Dr. Jekyll and Mr. Hyde.
In this chapter, Utterson goes to talk to Dr. Jekyll in an attempt to find out what is going on with him and Hyde -- why he has written the will the way he has. But his conversation with Jekyll really only makes things worse.
This is because Jekyll does not really tell him anything. He tells Utterson that it is a private manner and he should leave it alone. But at the same time he talks about how he can get rid of Hyde whenever he wants. And all the time, he has a "certain incoherency of manner."
So Jekyll is sort of just babbling a bit and doesn't really give Utterson any more information.