Clay,
I have heard some people say pillow cases should never be used as snake bags because they will not stand up to the pressures snakes can put on the seams. I have always been rather amused by that because pillowcases are purposely manufactured to stand up to lots of pressure over and over again. They get slept on, pounded by fists, beaten, shaken, fluffed up and so forth and always take it; and if my fat head does not ruin them - well a snake sure won't (I am talking quality pillow cases not a .99 cent special). I use em all the time for nonvenomous species, and have never had an escape from one yet because it got through a seam, unless the seam was faulty beforehand. (Seams are always a weak point to check on any snake bag.) I have also used cotton laundry bags - also very strong if you buy the right type. I imagine that for hots you would want a bag that is plenty long to be able to give it at least a few good twists, and still have the snake hanging a good distance down away from your hands before tying a knot in it. I like the bags on the wire hoop, wire hoop connected to a pole thing. Those are some long bags.
As for letting snakes out of the bag, I like your method of cutting the bag and not trying to undo the knot. I don't keep any venomous but I have caught a few on my journeys here and there. I always handle them with a lot of care and respect borne out of my fear of being bitten. One of the scary things was bagging them when I decided to keep one for observation for a few days. I may never have thought about being able to be bitten through the bag except that I had read about the possibility in some old snake collector's book (maybe a Carl Kaufeld book or something similar).
About a year or two ago, I was watching O'Shea on TV. It was an episode of his show where he was island hopping on a sailboat in the Pacific or Indian Ocean. He had a small viper of some sort in a bag, and took out the bag to check on the snake and wham. Tagged one of his fingers I think. One of the first things he said was what a jerk he had been to let a snake bite him through the bag, and that he was mad at himself for having let it happen. Luckily he wound up ok in the long run, but you could tell he was pretty scared even though the snake was not known to have a very toxic venom. I have been there and done that in as far as wanting to kick myself in the head for having done something stupid that led to me being hurt, but I hope never to do so with a venomous snake.
In fact I stopped collecting venomous at all because of something I read somewhere, that should have been common sense yet I had never thought of it. I always had caught them while I was alone in the field. I only really ever looked for venomous species when I was away from home on a temporary work assignment to places like Florida, Arizona, California or Texas; and no one else from work ever wanted to go out with me except on one occasion. There were lots of venomous snakes where I was at, so I would catch a few. This was a very big mistake, and could have proven to have been my downfall had I ever been bitten. Having someone else there to administer first aid, to call for help, to drive you to a hospital, to tell the doctors what type of snake bit you if you become unconscious, could all be crucial to survival. Of course I could still be bitten while out herping for nonvenomous species, but that is a risk I take much like crossing the street. I no longer tempt fate by seeking out venomous, and if I find em while alone it is 'look don't touch'.
Sorry I am really getting off of the original subject here, but I guess it all speaks to being very careful in handling venomous species when you handle them, and especially when shipping them as you are putting not just yourself but others along the shipping route at risk.
All the best,
Glenn B