Chinese vampires (jiangshi) tend to have a stiff and erect posture, not bent, with arms fully outstretched and reaching out:So that probably doesn't resemble elderly or frail so much but their sensory perceptions are extremely limited since they're blind and navigate by smell and hop around to move. So if we imagine a blind biped navigating by smell and hopping around, that kind of body language might make sense to help them navigate, reach out and feel their victims, that sort of thing. At least it's kind of makes some natural sense to me if I imagine I'm blind and navigating this way while standing on two feet and hopping all over the place and imagining not only my posture but what looks rather frightening.
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Props to you for finding pictures of "real" zombies
And the hands are just to make them scarier no one wants to get grabbed by a zombie