Some human behavior never change, such as the urge to doodle in the margin of a book. Historian Erik Kwakkel discovered this simple truth while pouring over some of the world’s oldest books and manuscripts at Leiden University, The Netherlands. Kwakkel is fascinated with “pen trials"—small sketches, doodles, and practice strokes a medieval scribe would make while testing the ink flow of a pen or quill. They usually involve funny faces, letter strokes, random lines, or geometric shapes and generally appear in the back of the book where a few blank pages could be found. Kwakkel finds them interesting because a scribe tends to write them in his native hand, rather than the stylized script they adapt when copying text.

“In some sense, these sketches are like fingerprints or signatures, little clues that reveal a bit about these long forgotten scribes who copied texts but who had no real opportunity to express themselves while working,” Kwakkel told to The Colossal.

A 15th-century doodle in the lower margin of a manuscript containing Juvenal’s Satires, a popular classical text used to teach young children about morals.