Books are items that can be read to your pet to gain intelligence and Alchemy Points. Each book grants +1 intelligence, with the exception of Book Package, Haunted Bookshelf, and Giant Book Of Subetan Classics: Abridged. These grant +6, +3, and +2 intelligence respectively.
Every for every 16 intelligence points earned, one Alchemy Point is granted. If you would like to maximize the Alchemy Points your pet has, be aware when reading any of the three books above; the Alchemy Point will only be granted if the landing stat after reading is the 16th, 32nd, 48th, 64th... etc.
See List of Books