Gentle Corn Snake Becoming Aggressive?

Question
I can't stress this enough... my snake has always been gentle and easy to handle, and has never tried to bite me or anyone else before. I made the mistake of feeding him in his tank when I first got him about a year and a half ago, and when he began to think my hand was a mouse, I realized my mistake and began to feed him in a box. Everything has worked out since then, until now.

I usually feed him every two (sometimes three) weeks with a small rat about as wide as he is. The last two feedings is when I noticed that, every time I opened the tank, moved around the tank, or stuck my hand in it, he jerked his head up and around the same way he does when he's looking for his meal. The first time he did this (Second to the last feeding) I waited until his head was on the other side of the tank and grabbed his tail, and once I touched him, he knew it was me and we were fine.

The next day, he was back to jerking his head around in search of prey. I left him alone for about a week, then decided that maybe he was still smelling the rat in his fecal droppings and bedding. I had to use a hanger (I did this carefully, I love my snake) to put him in his box and I cleaned his tank out thoroughly with warm water and a sponge, including all his hide outs, branches, rocks, and his water bowl. It didn't help.

After that, I decided that I hadn't fed him enough, so I fed him again. Still didn't help. I tried one more time to reach in and touch him so he would know it was me. When I grabbed his tail, and he seemed to act normal, I carefully pulled him out and he opened his mouth like he was trying to bite at something, but he didn't exactly strike at me.

He hasn't really struck at me at all, but like with all my pets, I know his body language and I know that if I stick my finger up to his head I will get bitten. This is my first time owning a snake, so I really don't understand what could have caused this sudden aggressive behavior, if you could call it that. I might also add that almost a year ago I switched him from live mice to frozen mice, but he never showed this kind of behavior before.

Oh, two more things. It's winter here, but I don't think that has anything to do with it, because this behavior didn't start until this month, and it's been winter for about three or four months now. Also, I just remembered that I usually handle him at least four times a week, usually more, but the last month or so -when this behavior started- I've hardly touched him. But before this, I've left him alone for longer and he never acted like this.

Answer
Hi Amber,
  I am not sure I have a good answer for you. I have several snakes that act that way. They used to be gentle, and they turned, although I treat them exactly the same as the all the others. I do believe that snakes can sense fear. I would start a routine and stick to it. Let the snake know that you mean him no harm. Do not fear any bite from a corn as they are not painful. When you reach for him, show no fear. I would feed him every 7 to 10 days. I would not worry about the change in attitude. Snakes are weird and hard to figure. I have 2 Macklot's that are little mates and their personalities are 100% different. Sorry I do not have a better answer for you, but there are things that we just don't know.