Bible Question: What was the First Sin?

anyone..This is a little off subject...but... I'm not sure what you all think of the serpent, or who it is. But isnt it kind of odd that eve is not surpised that the serpent talks to her? ( i get this from the text, it does not indicate that this has not/has happened before, and normally most people would freak out if an animal would talk to them.) And....is the serpent an acutal serpent? or is it another name for Satan. (i thought someone said somthing earlier about the serpent not being posessed by satan, so I was just wondering who they thought it was then.)
And since Eve does not appear to be startled by the serpent talking to her, does this mean that it was a regular thing?