One of the representative poisonous snakespoisonous snake commonly found in Japan is called the mamushi (Gloydius blomhoffii).

Mamushi lives in mountains found all over the country, and not a few people are bitten and died.have died after being bitten.

The poison is blood poison that affects bleeding and thevenom affects the blood and cardiovascular system. OR The venom affects both the circulatory and cardiovascular systems of its victim.

Snakes are venomous and produce venom; plants are poisonous and produce/emit poison. I know, it's pedantic. Please forgive me haha.

HoweverInterestingly enough, dogs don't die byfrom the poisonvenom.

This is a suggestion; a transition to make it sound more natural. Your original sentence was grammatically correct, for the record. (I would have probably written "However, dogs don't die from the venom.")

That being said, the dogs bitten by mamushi are swelled on their faceey aren't immune, however: a mamushi bite causes intense facial swelling.

The appearance looks regretting and it's funnyis swelling is as humorous as it is pitiable.

That is admittedly a formal suggestion. Another option that sounds more natural but changes it more: "In fact, it's so intense that it becomes both pitiful and funny."

You can watch these kinds of dogclips of a few unlucky canine victims on YouTube.