The Bloedzuiger‘s habit of releasing a toxic cloud of acid upon demise that not only wounds the Witcher, but every other monster within range, is not a particularly strong Darwinian survival tactic – particularly since it will wound other Bloedzuigers. You’d think that these things would be able to handle their own stomach reagents.
Also: The Witcher is fun, but it’s also kind of messed up in the head in some ways. How’s the sequel? – Not that I’m probably not going to buy it anyway.