If somethings poisonous, it means you get sick or die from ingesting it yourself, like if you ate a poisonous berry. If something wounds you (like bites, stings, ect) and therefore enters your body and causes harm, that’s venomous, like venomous snakes or scorpions. Things tend to be one or the other, but something can be both poisonous and venomous. A simple way I saw to describe the idea is “if it bites you and you die, it’s venomous. If you bite it and you die, it’s poisonous”
And yes exactly, male platypuses can paralyze other male platapuses on fights during mating season. That lets the winner get the girl ig