The Sharingan is a rare trait that only occurs in a few members of the Uchiha Clan.
The Sharingan is a rare power that resides in the eyes. The user of this visual Jutsu or doujutsu can instantly see and comprehend any Genjutsu, Taijutsu,and Ninjutsu and reflect the attack back on the attacker. The Sharingan is a special rare form of doujutsu. However there is more to the Sharingan then that a lot more. The Sharingan can analyze an opponent's technique and then copy it to the smallest detail.
The Sharingan can not fully neutralize the Silent Killing technique.