It is almost certainly something you have repressed (pushed down from the conscious mind into the unconscious). We repress what we can’t cope with, but the anxiety or guilt-feelings that caused us to resort to repression do not leave us: they linger and fester in the unconscious and, if not given conscious attention, will have destructive consequences. Don’t let yourself be constipated psychologically. Get rid of that store of negative emotion - resentments or whatever.
Anxieties and guilt-feelings often have irrational beginnings in early childhood, though they may remain dormant until some later experience wakens them. An emotionally detached appraisal of the situation that first gave rise to them may dissolve them.
If not, seek help. Alternatively, adopt a Gestalt approach: don’t bother about the origins of the negative feeling; just see what it is doing to you - and others - in the present, and deal with it, expel it like faeces, here and now.
(2) Excrement may be a symbol of something you disapprove of or despise - perhaps mistakenly. Take a good look at the excrement to discover precisely what it represents in yourself.
(3) According to Freud, faeces may be substitutes for either the penis or a baby. This is more applicable to a woman’s dream than to a man’s.
(4) Excrement may symbolize money - ‘filthy lucre’ (‘He’s rolling in it’; ‘She’s stinking rich’). [1]
If the excrement is transformed into living animals, maybe rats, you are accepting that you are responsible for managing your own impulses. Excrement in its more spiritual meaning belongs to the realm of feelings and you may simply be trying to get rid of bad feelings. Those bad feelings can be turned into something worthwhile. Evacuation of the bowel usually highlights our need to be free of worry and responsibility, or possibly the need to learn how to be uninhibited. It can also signify the sexual act. [2]
See also: Intestines, Colon. Toilet. [4]
Stepping on dog poop in a dream promises windfall in business. [5]
As with all dream symbols, the tone and setting of the dream indicate which meaning is appropriate. [7]