I've had my tegu Marty for about two or three weeks and I'm still having trouble getting him to open up to me. I pet him in his cage all the time and when I go to pick him up he gets worked up and it gets hard to hold him but he likes being in my sweatshirt. Recently he's starting to get more angry he's hissing at me and thinks my fingers are food. Is there anything else I can do? I see all these stories about how tame and how they crave attention but mine , not so much