I am doing a suvery on this subject right now.
I believe the whole "don't feed in cage thing" is a myth, or at least not as needed as some people toss around the idea. And certainly not normally explaned correctly. IMHO
For one, I don't believe the snakes can become accustomed to your hand being food when placed in cage if you are doing proper husbandry. Let's say you fed your snake IN cage once per week. Then you also change water once per week. You clean cage once per week, and you handle your snake twice or so per week. That's a total of 4-6 times of putting your hand into the cage. And out of 6 times the ONE time you fed a mosue, this is supposed to condition your snake? Not in my mind. IF you are handling often. etc.
Also, most feeding accidents occur when the snake is being moved from this oh so wonderful feeding tub back into the cage. Not only is this stressful, but my unfinished survey results (which yes is only a personal thing, not perfect) also indicate most people have accidents while moving snake from feeding tub to cage. Which makes sense, common sense.
Also people like to say "conditioned" that food is coming. How can they explain the differance between feeding them in cage and picking them up outta cage? If snakes are sooooo conditionable by only ONE feeding per week in cage, don't you think they would also be sooooo conditional and think each and every time you remove them from cage they are getting fed? They don't though. And it doesn't make sense than every snake would condition itself the opposite way, and think food is coming IN every time if they don't also believe each time they are coming out of the cage they are being fed.
Another point is that many many people including myself feed in cage. None of my snakes have become more aggresive. I beleive if a person starts feeding out of cage and thinks "hey my snake is getting friendlier" that the reason it has calmed a bit is because feeding in tub gives you two extra pick ups/handlings per week right there! This WOULD be a good reason for tub feeding IMHO. That and preventing substrate ingestion. But as for aggresion, I think its fooey, and it opens people up to bites.
Remember just MHO and hopefuly I can post the results of my survey soon. I am not saying its wrong, I am jsut giving my opinion.
bmm