Surely "you have his blood on your hand" is also correct? The given answer (hands plural) presumably is figurative.
Why wasn't hand in the locative case?
It is. You need the peculiar dual endings for body parts here. Check the tips and notes.
You mean the tips and notes for the Dual skill below. There are no tips and notes for the Body skill (yet).
Is the Czech sentence literal or figurative?
Could be either in either language.