maverick-ornithography:

Of great interest to scientists studying quantum phenomena, Horses are one of eight known multidimensional “keystone” species extant across the explored multiverse. Unlike most fauna whose multiplanar existences branch as they age, Horses begin their lives simultaneously existing across nearly infinite timelines which gradually collapse into a single life-line or “trunk”. Early research suggests this ‘backwards’ tree-of-life to be an evolutionary counter to their otherwise astonishing fragility; by starting at a massive existence advantage these quantum-entangled Equidae are better able to weather their nearly constant murder on the extradimensional level.

Unfortunately, this has the knock-on effect of every Horse having total awareness of their thousand daily deaths. This is why a Horse may suddenly startle at a discarded shopping bag or refuse to enter a trailer for transport; in a close worldline that Horse was consumed by a carnivorous Land-jellyfish or maliciously led into the maw of a Deathslug worshiped by the local human-analogue.