Maybe "believability" is too strong a word. It supports the Suspension of Disbelief.
I admitted that Hibino's remark about how wood can be so flexible (yet crush stone, dent and tear metal, etc.) was something else. Certainly connected to the mysterious power source that allows these to teleport, shoot energy or electrical blasts, change form, and so on. Despite all these fantastical abilities and their remarkable durability, the kakashis' movement is all rooted in being like a Karakuri ningyō or European Renaissance era puppet/automaton, similar to Leonardo da Vinci's robot from the mid-1400s.