Tweethi there mate, im a newbie as well as far as AS goes, but i work in a hospital where i take blood alot.. if your in a vein the syringe will fill very quickly so if you can draw off more than 1cc of blood your a bit close, usually you will just get a small bit of discolouration from small capallliary vessels that have been punctured on the way in and sometimes a tiny air bubble will enter the syringe, then your in a muscle and not inside a vein..