Someone got mad at Mark Twain's complaints about the illustrations created for Huckleberry Finn, so they modified a drawing of Uncle Silas, showing him with an erection poking out out his pants fly. Most of the copies were destroyed, and those that remain are worth tens of thousands of dollars in the collectors' market.
The first run was being printed, and advance copies were already out being shown to potential customers, when Webster got a panicked letter from a salesman in Chicago. When the salesman cracked open his sample of the book, he found that someone – maybe a mischievous printer, or one frustrated with delays; maybe Kemble taking revenge for the rejected drawings – had made a last-minute addition to one of the illustration printing plates.
In a picture of Uncle Silas speaking to a young boy while Aunt Sally looks on with a smile, Silas sports a crudely drawn penis, or at least a shadowy bulge in his pants.