One word:
Wookies.
Really though, if you're going to enslave an entire race, wouldn't you choose one that can't, oh I don't know, rip your freaking arm off if the restraints fail for even one second?
Wookies.
Really though, if you're going to enslave an entire race, wouldn't you choose one that can't, oh I don't know, rip your freaking arm off if the restraints fail for even one second?