If anyone wants to know, the reason that happens is because spiders move their legs with a hydraulic system and once they are dead the pressure gets released and they revert to their “default” state.
https://asknature.org/strategy/leg-uses-hydraulics-and-muscle-flex/
Dont tell anyone I told ypu about this…
https://roddenberry.x.io/2369-deep-space-nine-ds9/