So I adopted Cyrus from about 3 weeks ago things had been going amazing until about half an hour ago. My sister was cleaning off the end table in the living room and went to grab an empty container of pudding. As she grabbed it Cyrus bit her wrist and thrased violently. Luckily she had on 2 sweatshirts but he bit with aggression tore the first one and her wrist is bruised and swollen. I yelled and grabbed him and he let go but I just don't understand and now sister won't go near him. He was amazing no food agression I hand fed him first week to make sure and he's been great with all people and dogs but now I'm working on convincing the family he's not an aggressive dog but mom and sister are afraid and want him to go. I can't get rid of him I'm attached but need help in explaining this somehow. Any input would be much appreciated!!!

I had the same problem with kirk when I first brought him home. He was under the impression that everything in the house belonged to me and no one else had the right to mess with anything. Over the first few weeks, both of my roommates had reason to discipline him because of one thing or another so all 3 of us have established ourselves as his alpha I guess. The problem went away after that. Biting back seemed to work really well for me too. If he ever bit me, I'd grab him and bite him on the ear. They learn quick that way.

Heh. I think that's honestly the first time I've seen that referenced online. Wouldn't recommend it.

If your family already has it in their head that he's aggressive and react to him submissively, you have a big hill to climb. He has already learned that his behavior netted him the result he wanted; her to go away. Your going to have to make them a positive thing in his head, probably by pumping him full of treats for not reacting to them. And they need to not be afraid of him. But I don't get fear of dogs anyway so trying to address that would not be in my repertoire.

Was he licking the pudding cup? How close was he to it? Was it a quick grab (by the human) to get the pudding cup?

First off being afraid of the dog isn't going to work. If anything it will make things harder. To bite and shake (especially a human) is a pretty serious thing and I would really recommend getting a trainer out. There are things you can do and steps you can take but I feel it would be better for you all to have a professional there with you to actually see how Cyrus interacts and what can be done to prevent these problems and perhaps remedy whatever the underlying issue is.

Most information I feel comfortable giving is don't let them be fearful because that 100% will make things worse. Perhaps leash him while he's inside so he can be moved easily and made to comply without the worry of being hurt.

Yeah i would not suggest biting your dog either after them "attacking you" now putting them in time out either in a crate or another room or a spot on the floor yes. and i think your mother and sis need to step up and show alpha, things like them feeding, walking, giving treats to Cyrus. Let him know that all of you are in charge and not just you. like eddy said make Cyrus feel that they are a positive thing in his life as well as you.
Sorry that happened to your sis but you all need to work with him to prevent that from happening again.

Thanks guys I was kinda thinking about the alpha thing with me and my father he does nothing but listen no nipping begging anything so have to get the girls in the family to show him he's below them in the "pack". And Kristina he was close to it probably 6 inches away but her hand was already around the cup to take it away it was when she did that he lashed out. Going to have the girls in the house work on showing him who's boss so to speak thank you guys.

Have her and your mom feed him for a while - the leaders control the resources (food). It'll remind him who is the leader. Have him sit, put the bowl down, look at you and then give him the command to eat (ours is "ok!"). If your sister is ok with it, also try "tethering" - having him on a leash attached to her for hours on end. He has no choice but to follow her around. Works wonders!

Started with hand feeding today will try the tethering thing also sounds kinda fun haha thank you for all the help expecting some positive reults