Amazon is currently having a buy-one-get-one free promotion on Dr. Seuss Books. You can view all of the Dr. Seuss books here, and you should see the free book discount automatically in your cart at checkout.
Check out all of the Dr. Seuss books here.
I believe the sale is actually buy 2 get 1 free, not BOGO. Still a great deal on Dr. Seuss books though, and free shipping for orders over $25!
I just checked again and added Green Eggs and Ham and The Cat in the Hat to my cart, and at checkout it is discounting the order $8.99 (price of one book). The BOGO deal might only apply to certain books, not the multi-packs?