Let the four books of A's novel be 1234, and the four books of B's novel be 1234. Just 1234 and 1234 should be opened separately.

When 1234 is on the left and 1234 is on the right (the order is uncertain), * * * has A44*A44=576 cases.

When 1234 is on the left and 1234 is on the right, there are also 576 cases.

Therefore, there are 576*2= 1 152 that satisfy the meaning of the question.

That is, the probability is1152/40320 =1/35.