In recent Naruto chapters (5 kage summit arch) it was shown that
All members of root (the foundation) have a tattoo on their tongues preventing them from speaking about danzo. This is done so that nobody is able to tell anyone about danzo's secret motives and plans.
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. As i was re-reading the manga however, i came upon the chapter where sai, yamato, naruto, and sakura invade Orochimaru's lair. Here, sai spills his guts about everything that danzo is planning.
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How is this possible with the tattoo on his tongue?
Nice catch! 