Another thing I picked up on is that the boy may misbehavebe disobedient is because he hasn't learned how to express his anger and frustrationsemotions. HeChildren at 5 years or less are may have have not been taught the wordsknow how to match his emotionsexpress anger, orfrustration, hunger, tiredness, overwhelming, boredom, etc. Or worse, heif the child has been physically abused by an angry adult. In such a case, spanking could be learned as acceptance to hit someone when they are angry, especially if the child doesn't understand why they are being spanked.
I used to ask my own son why he was hitting, and he also told me "I don't know" with a confused look on his face. What he did understand was "hitting hurts". I asked him if he wanted to hurt me or the dog, and he shook his head no saying, andthen said he was sorry with tear filled eyes after I told him he did hurt me or the dog. Then I asked him how he felt before he hit so that he can learn words for those feelings. Then I taught, and helped him decide what he canwill do instead when he feels that way again, such as going to a quite place, hitting a pillow or physical activity, or talk about what is upsetting him, etc. Now when my son is angry, he will shout "I'm mad at you!" and walk away for a time out to feel and think until he is ready to talk more about it, or he starts playing when he's over what he can't change. We are still working on not needing to shout when someone can hear his normal tone, but it is a work in progress.
Another possibility is that your 5 year old could be disobeying TO GET a reaction out of you. Whether it is for attention, or to get a reaction, they are learning how to manipulate the situation through the cause and effect I mentioned earlier. The best defense for this is to try to prevent situations where the behavior tends to occur, such as keeping him separate from animals and small children. Then try to not over react to his behavior, because you could be positively reinforcing the behavior by your actions, therefore increasing it. Sometimes to stop bad behavior, you have to ignore it or keep a poker face when you can't. I've walked away while my son throws newly folded towels on the floor, because when I told him not to, he would continue to do it while smiling at me. Now if he doesn't stop, I'll take away his favorite toy, and he doesn't get it back until he folds all of the unfolded laundry, and puts it away no matter how messy it is in the end.