In "The Black Cat" what earlier mention of violence foreshadows what the narrator does to his wife?

I am
assuming that you are referring 's short story "."  The narrator explains that before
his drinking problem, he had been a very nice man, amiable, with a fond love for animals. 
However, his drinking effected a pretty drastic change upon him; he became irritable and
violent, lashing out at his pets, and even beating his wife.  Any one of those acts might be ato
the brutal murder that he later commits. One particular incident is when his black cat, Pluto,
bites him as he grabs him violently.  The narrator becomes incensed with rage, and without
thinking,

"I took from my waistcoat-pocket a
pen-knife, opened it, grasped the poor beast by the throat, and deliberately cut one of its eyes
from the socket!"

Fortunately, the cat recovers from
this incident, but the narrator showed his tendency to inflict severe harm in fits of rage. 
This foreshadows the later, much more dramatic fit of rage that later ends with his wife
murdered.  He laters hangs the cat, but this incident was done calmly, with "tears
streaming" from his eyes, and not in a violent fit of anger, like with the original
brutality--the original harm to the cat mimics more closely his state of mind when he kills his
wife.  Later, he takes an axe to the other cat that had followed him home one day--this raising
of the axe could foreshadow what happened next:

"Uplifting an axe, and forgetting, in my wrath, the childish dread which had
hitherto stayed my hand, I aimed a blow at the animal which, of course, would have proved
instantly fatal had it descended as I wished."

Instead of killing the cat, however, as his wife tries to stop him, he turns on her and
kills her instead.  On the whole, given the narrator's tendency to have violent fits of anger
and rage, and to beat his wife and torture his animals, the end result should not be as
surprising as it could have been.  I hope that helped; good luck!