Al's body should not work

To be honest, it shouldn't work. The show tries to have rational and logical points throughout for most things. However, one major illogical point is that a soul bound to an inanimate object like Al's suit of armor, causes that object to be able to move etc.

Let me explain:

Al does not need to sleep, eat, etc and does not get tired. This is because he has no brain or muscles to fatigue and does not rely on food for energy. By this logic, he should not be able to move (due to not having muscles), speak (due to not having a larynx which produces sound in humans). It also makes no sense that because he has another piece of metal attached to him that it becomes part of his body that he can move and manipulate. When they add his head it moves, when they add his hands he can move them. Why then can't he touch a cannon and it would become part of him?

If it were completely logical, that flat part of the armor suit that Ed binded Al's soul to would be the only part that contained his soul and he would be unable to speak or do anything really. It would just be a living piece of iron. Obviously it would make for a completely boring show but this is just something that bothers me as I rewatch it.

Edit: clearly most early commenter are missing my point and I guess it is my fault. I am speaking on logic within the series. Obviously alchemy, and everything else is fiction. I'm just saying this particular part has no explanation unlike everything else. There's real life logic and logic within a work of fiction. I'm speaking on the latter.