držet + Accusitive ?
držet (se) + Genitive?
Am I right?
Technically, "se" is in accusative (while "si" is in dative), so this reflexive pronoun already takes up the spot of the direct object (=accusative) in the sentence. That's why verbs with "se" don't take accusative nouns.
My answer "Proč držíš tamhleten šperk" wasn't accepted :(
Well, it is really strange. Tamhleten is something (over)there that you can see (hle = see). It is quite a strange combination with something you are currently holding.