My Boa Is Angry and I Dont Know Why

Question
Hello,
I have owned a red-tail boa for a little over 3 weeks now.  He was completely fine for the first 2 weeks but lately he's been getting angry a lot.  He'll hiss and open his mouth pretty wide even when I'm just going in to his tank to replace his water and such.  I have completely new substrate that I need to put into the tank but I'm afraid to get him out.  He was fed a big meal 2 weeks ago, so I know that he's probably not hungry.  As far as I know, his temps are okay.  We have a heating pad under the tank under his hide rock and also a basking light that we turn on during the day.  I am just curious as to why he is all of a sudden angry all the time.  Any suggestions on what to do would be appreciated!

Answer
Patrick,
  Chances are he is not angry, he can sense your fear. Put on some garden gloves and reach right in to take him out & replace the substrate. They get hissy sometimes, I do not think anyone is sure as to why. If you are consistent and fearless, he should calm down over time. The do tend to get more calm as they get older.