On the "abracadabra" example? The overwhelming majority would come from the possibility that any time anything whatsoever happens the world is "destroyed", for some weird, maybe anthropic use of the word "destroyed" I don't understand compatible with me still being here.

If we limit it to "abracadabra" and nothing else, that's complex enough that < 1/trillion just picking it out of hypothesis space (lots of combinations of sounds that could destroy the world, lots of things that aren't combinations of sounds).