Dreams and visions about a crocodile are about birth, fertility, changes, primal mother feelings and also protection of the highest form you could wish for. The crocodile is a projection of your own character traits. So you have to become aware of all your fears, pent-up aggression, pains, anger and sadness that you have to express. An alternative explanation is a warning of hidden danger and obstacles you can experience.
If the crocodile attacks you or opens its mouth in your vision or dream, it means that you attack yourself, that you become aware of your anger, aggression, sadness, fear and problems that you do not know how to overcome. An alternative explanation is that you have not been really sincere in expressing your emotions and crying crocodile tears.