Is bakancs an irregular plural or does it refer to one single pair of boots?
In general, things like (pairs of) pants and shoes and boots are singular in Hungarian. Multiple pairs are of course plural.
If you think about it though, the snake is probably only in one of the boots ... not a hat it would make any difference to the Hungarian sentence.
I think you could say something like "egy kígyó van a félbakancsban" in this circumstance. But there are folks who are more expert than I.
Even if bakancs always implies a pair of boots in Hungarian, the correct translation into English would be "boot."
Well, "pair of boots" would also be completely ok, and "boots" is good enough that it should be accepted.