awww love bites
yesh, they do this sometimes.. so many variables as to why.
as previously mentioned, it could be a specific scent on your hands, it could be wanting an upgrade of food size..
what you can do if it is a scent thing, is get a specific type of soap or some anti-bacterial hand stuff like 'aquim' and use it before and after every single time you go to handle him/her.
but before feeding dont, this will get the snake into the idea its about to get handled rather then its about to get fed.
hope that makes sense haha
Nat