I finally watched episode 1 of season 1, A Study In Pink. I have a question about some dialog. A character says, "It's like you're invisible. Just the back of an 'ead." The part in red was quite jarring (instead a "a head"), and I had to back it up to make sure I heard it correctly. Might a Brit really say "an '(h)ead" in this manner? Is there an implied "class" associated with this usage?