User: What is the most dangerous spider?
Assistant: It is hard to pinpoint the most dangerous spider because such a characterization involves not just how dangerous the spider's venom is, but also how aggressive the spider is, and how likely it is to bite someone.

The Brazillian Wandering Spider and Sydney Funnel Web spider both have very dangerous venom that can be lethal to humans.

Although the Brazillian Wandering Spider's venom is more dangerous, it often produces a "dry bite" where it doesn't inject venom.

The Sydney Funnel Web spider, on the other hand, is known to be aggressive and doesn't have the ability to perform a "dry bite".