It will hiss and open it's mouth
When your parakeet is about to bite you he will probably open his mouth and lean toward you. He will be agitated or scared (and in a bad mood ).
Parakeets bite for many reasons. Did you just get your parakeet and he is scared? Perhaps your parakeet is very protective over a certain toy. It could also be because they are pregnant or are protective of it's other parakeet friend. Are you feeding your parakeet? Cleaning his cage, feeding him things other than seeds? You have to put yourself in your parakeets shoes, because depending on an individual bird they may bite for various reasons.
His/her mouth is open.
YES!
I believe that when a parakeet is mad their feathers pufup not sure sorry
the only way to know that is to see if it is going to bite anything... get a stick and put it softy on its nose and if it does not bite the stick then it is not going to bite you...but to make sure...pick it up by the back of the shell...just in case; at least for awhile.
it either doesnt like you or it has a certain need or problem.
It is very rare that a parakeet right from the store is going to be nice or even perch on you hand. It take a while for them to trust you. You have to prove to them that you are not going to hurt them.
well, actually nothing. Your parakeet may also lay eggs but, the eggs AREN'T going to hatch. :(
An animal can bite. for example when a lion attacks he's going to bite you because an animal doesn't know how to do something else.
Probably when they are very affectionate with one another or you have baby parakeets.
You don't introduce a Parakeet to another Parakeet. They get to know each other on their own, They might make a flock and start grooming if they start fighting and draw blood have a extra cage to separate them.