Upon picking up 3 items from the following list, Isaac will fire tears out of both eyes simultaneously 25% of the time. This effect stacks with items such as 20/20, The Inner Eye and Mutant Spider, multiplying the number of tears.
The chance of firing double tears is not affected by luck.
On use, spawns an orbital Wisp familiar that fires spectral tears but can be destroyed. Also becomes a passive item that causes other active items to spawn themed Wisps.
As Jacob and Esau / Tainted Lazarus, it's not possible to cycle between three books to give both characters the transformation's effect. Each character needs to pick up three different books, meaning six books in total.
Most likely due to the fact that Keeper's triple shot is innate and not from The Inner Eye, Bookworm will only add one tear to his shots, instead of three. This may be a bug.
A bookworm is a person who's devoted to reading, especially books.
Book of Virtues is the only passive item to contribute to the transformation.