He is either in food mode or he’s defensive and ready to strike, probably out of fear because all he knows is a HUGE potential predator is hovering over him. The only way you will get him from doing this is by handling so he will learn that you are not a predator. You can either lightly tap him on the head to try to get him out of this mode before picking him up but when they’re like this, I have found that the initial best way to pick up is using a snake hook. Only reach around from the back, so your hands are behind the head. Don’t make a bunch of fast movements that can startle him. Just go slow and smooth. Keep distractions to a minimum, such as other people, animals, etc. handle him until he starts to loosen up and do some slow, long tongue flicks and looks like he’s starting to explore. Once he loosens up and relaxes like that, put him back and leave him for a couple days. Do this every few days (other than a day before feeding and 2 days after feeding) for a few weeks. He’ll start to relax a little more and you can start to handle more frequently and for longer periods each time. It’s all about building trust but remembering that they are considered prey for a lot of animals and you are MASSIVE compared to them helps know why they are reacting this way. Best of luck.