two questions about corn snakes.

[ErikBush97]

Hi, everyone. One of my friends own a few corn snakes and he didn't mention that until I mentioned that I just got one on the fourth. Anyways he said that his 3 footers are all around 500-550 grams. Mine is 2'6" at the shortest, probably 3'6", and 4'0" long at the most... haven't measured yet.. but mines 170 grams. Is that under weight or is that fine? Also my second question... the snake has been really great and VERY tame since I have gotten him/her. However I fed it on Saturday and he's been rattling at me every time I am close to the glass. I understand that he's digesting, a little slower than usual, and probably feels a little vulnerable, but why's he only showing defensive behavior after eating? Think he's still on the hunt for food? That'd make sense if he's/she's under weight as I thought.