IF YOU DONT WANT TO KNOW ANYTHING ABOUT THE UPCOMING NEW EPISODES DONT READ
above is a link to a promo trailer and at 29-31 you hear and see Rick as Michonne "You think he's crazy?" and Michonne replies "I think hes dangerous. At first I assumed they were talking about the governer but when taking a closer loo, they seem to be in Morgans old house seeing as you can see a sniper rifle mounted by the window. I think they are talking about Morgan
SPOILER IF YOU HAVE NOT READ THE COMICS STOP READING
If youve read the comics than you know that at some unspecified time, Duane became a walker. I think in the show when they revisit Morgan theyll find that this has already happened leading Morgan to kind of lose it and start writing all over the walls as you can see in the background of the promo. Leading Michonne to accuse him of being crazy.