After burning the Force tree in front of Luke, our little green friend says the following about the sacred Jedi texts:
Read them, have you? Page-turners, they were not.
How does Yoda know that those books are not page-turners?
Had he read them before dying? (and if so, how?)
Can he "read" them through the Force while being dead?
Is he just joking and has no idea what's inside them?