Spoiler Alert: For those who haven't seen episode 366 of Naruto Shippuuden.
As shown in episode 366 of Naruto Shippuuden, Orochimaru was able to restrict the movements of nidaime hokage Tobirama. But he mentions that Hashirama could have undone his binding at any time.
My question is why didn't Hashirama undo the binding during his reanimation at Chunnin exams?