independent arm from body - unity2d

Hi there!

Im trying to figure out how i can make my character have an independently moving arm while the body stays the same.

For example, i want my to always look at my mouse position, but the body shouldnt rotate with it. A good example would be this: https://www.youtube.com/watch?v=KfucMk56D4A

a somewhat good example would be this: http://www.miniclip.com/games/heli-attack-3/en/ however this has the whole torso move, along with the arm. i want just the arm, however this could also work.

Im new to unity, so figuring out how to actually make a character that is made out of more than a single sprite would be a good place to start with me, as all i have been working with till now was single sprite characters.

Thank you for your help ^^