it will probobly be due to the fact of feeling unsupported, even my big common boa, who is the softest snake i own will thrash about like a mad man if i dont pick him up right.
i dont know how big yours is but wit my big female i used to distract her with one hand as i mentioned before then use the other to slide in underneath through the coils so when you lift they tighten up onto you kinda without realising it then your a big warm perch lol.
the best tiome to try is when they are on the ground, trying to get these guys off perches is stressful for everyone involved lol.
heres a couple of pics of the big girl, she was a good 6-7ft easy and reasonably calm, only ever got me once and i still kick myself for parting with her!
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