Just about any animal is trainable. At the same time- no animal is 100% reliable. Sometimes dogs just won't stay.

My beardie sorta knows "come here" (way too many waxworms later).

Domestication is, however, a really long process. I think you'd have to have a pretty amazing bond with your snake to make it remotely feasible. But boas are smart- no doubt about that. The trouble is convincing them that they want to do what you want them too. Additionally animals that are largely kept in cages tend to be less trained than animals people are literally constantly interacting with (birds aside). My cat's behavior just affects me more constantly than my reptiles.

I would think (although I'm by no means sure) snakes would clue in more to visual gestures than sounds... could be wrong- probably varies from type of snake. But just a thought...
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1.1.0 beardies
1.0.0 bloodred corn
0.1.0 leopard gecko
0.1.0 golden gecko
0.2.0 mourning geckos
1.1.0 cats

soon to be:
0.1.0 amel motley corn
BRB!!!!!