From the piece:
Interacting with the eagle appears to be one of the central aspects to the game. You're free to touch the eagle whenever you like. Its reactions will differ depending on where you touch it.
There's a care aspect for the eagle as well. You can feed the eagle and remove spears and arrows that have pierced it. Ueda feels that the development staff will have to take care to strike a balance and make sure the care aspects do not becoming a chore.
Also, if you think that it's a rather strange looking eagle, then you'll find Ueda agrees with you: "It's important that it be 'a strange creature,'" explained Ueda. "We made sure and not make it too balanced."
More through the link.