ELI5 Snakes - does eating a venomous snake kill its predator?

What is the difference between venomous and poisonous? How do snakes never get in a knot and if they do, how do they untangle themselves? Why do snakes have such potent venom? What happens when predators eat part of a snake that contains venom? Why are snakes evolving to not use their venom?
... we explain like I'm five
Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: casperslakes, xychologist, freestyle-scientist, freebytes, qyle95, yesssssssssssno, cameltrowe and phage0070
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