To humans..
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Absolutely they are dangerous. However, there is no authenticated record of a human being having been killed by one of these snakes in history. There are of course people who have gone into the wilderness and disappeared, and it is always a possibility that they may have been eaten by an anaconda, but there is no solid proof that anyone has died this way. OTOH, there are many reported incidences of South Americans dying because of rabies caused by vampire bats, and of course even more deaths caused by venomous snakes every year.
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Yes, the can kill grown men by suffocating them.
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of course when they are hungry....