I found this here on tumblr originally, captioned

Rabbits between the staves. Cambrai BM 125-128, c. 1540-50

Then I decided to do a vibe check to see if this was legit. I used IMSLP (The International Music Score Library Project) to check and found the overall music here. I narrowed this down to Cambrai BM 127, the Bassus part. If you download the Bassus (Complete) file you’ll find this cute illustration on page 310!