This Cursed Seal is given by Danzō to all members of the ANBU subgroup Root, to ensure no information about Danzō or the organization falls into the wrong hands; something that would not only endanger the organization, but even Konohagakure itself. As Root was an organization of top secrecy, committing less-than-respectable acts in the dark to support the village, this seal was designed to keep it so.
When the wearer of this Cursed Seal speaks about anything related to Danzō, their entire body will be paralyzed, taking away their ability to speak or move. It is applied to the tongue and takes the shape of three solid lines and two broken lines from the back of the tongue to the tip, possibly a hexagram. It could either be the hexagram ䷞ (咸, Japanese: "kan," Chinese: "xián"), which can be interpreted as "influence," or it could be the hexagram ䷠ (遯, Japanese: "ton," Chinese: "dùn"), which can be interpreted as "concealment."
The seal can also be used during combat, as seen when Danzō grabbed Sasuke Uchiha by the throat, secretly applying the seal. Later on in the fight, the curse seal's marks spread around Sasuke's body, paralyzing him. It is possible that the seal removes the victim's ability to use all ninjutsu, as Danzō released his Izanagi technique after Sasuke was under the influence of the seal, even though his his Mangekyō Sharingan was still active, suggesting that Danzō believed that had no reason to feel threatened. Sasuke showed, however, that he was able to break the seal when his Susanoo reached completion due to his increasing hatred.
There is one last secret capabiliy of which this seal has, called the Reverse Four Symbol Seal. This is similar to what the Yondaime Hokage used to store away the Kyuubi; in reverse, this has the affect of sending out a mass amount of chakra into the vicinity to destroy anyone in the perimeters of him, Danzō, releasing it instead of storing away the chakra. In the event, this only occurs (or seems to occur) when Danzō is on his dying breath. This forces those nearby to be dragged toward Danzō to be sealed away with him along with his relinquishment.
