Itachi poked sasukes forehead everytime Sasuke wanted to train with him... Itachi said "Maybe next time" and poked Sasukes forehead, after this when Sasuke went to practice himself - he learned what he was supposed to learn.
When Itachi last poked Sasuke's forehead - Sasuke was given the Amaterasu (which was used against Obito automatically on contact)
what i believe, is that Itachi transfered jutsus/knowledge/skills into sasuke... without him knowing...
When Itachi last poked Sasuke's forehead - Sasuke was given the Amaterasu (which was used against Obito automatically on contact)
what i believe, is that Itachi transfered jutsus/knowledge/skills into sasuke... without him knowing...