Who was in the third summoned coffin?

[Arctyc]

You never actually see the third coffin in the manga. The summoning scenes are chapter 117, pages 17-19. The eye commenting is Orochimaru hiding behind the first two.

[Lithonite]

Orochimaru knows the power of the sharinganis its increased perception and it can copy all jutsu- as long as they are not bloodline limits. It can copy them assumiing the user of the eye can understand what the increase percection is seeing. Seeing as Orochimaru is a super genious, that kind of increased perception would be extremely benficia. granted yeah he probubly could summon all the great nin and ask them- but that wont help him unless the jsutsu he wants belongs to a dead Ninja. Not to mention im guessing but aside from difficulty of summon dead Nin, that such a tehcniue requires a huge amount of chakra.. chakra that he would need when learning and praticing a jutsu he was being taugh by his summon.

So since summons would limit not nly chakra availible to be taught a new jutsu it also is limited to fact his teacher has to be dead and he would have had to have seen or heard of the jutsu to know he wantd to learn it.. no learnng on the fly.. so to speak. Simply put the sharingan is the only way for ORochimaru to get what he wants.