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

I am assuming that you are referring Edgar Allan Poe's short story "The Black Cat."  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 a foreshadowing to 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!