my human group wants to spy on a person, who is actually an angel.

1) Is there a why that they find out that something is off? (I think that would make the story more interesting..)

2. a) If an angel gets hurt, how similar do they look to humans? For example does they mortal mask include things like bleeding? They only thing I know so far is, that they don't have internal organs. (CofD, page 129) So, what is there instead? What if someone cuts them really deeply or they loose a limb in an accident or whatever? How far are they similar to humans, and...