Rabbit blowing a horn. Among the marginal creatures populating medieval manuscripts musical animals are fairly common.
Royal 10 E IV, f. 3, Mermaid and merman
This is beyond bizarre - from the Luttrell Psalter, anonymous medieval manuscript known for its scenes of daily life and otherworldly beings.
From the Medieval #Manuscripts blog post 'Medieval Maps of the Holy Land'. Image: The Acre map of Matthew Paris
Prayer roll, MS G.39 fol. 11r - Images from Medieval and Renaissance Manuscripts - The Morgan Library & Museum
Unknown maker, France The Metz Pontifical, 1302 - 1316, folio 7r, A hare with a sling approaches a knight in chainmail, an absurd parallel to the story of David and Goliath.
Dancing, Harley 4425, Guillaume de Lorris and Jean de Meun, Roman de la Rose Netherlands, S. (Bruges); c. 1490-c. 1500
Detail from The Luttrell Psalter, British Library Add MS 42130 (medieval manuscript,1325-1340), f171v
Cat with a zither, from a Belgian Book of Hours, c. 1470.
Medieval Invite Illumination by ~dashinvaine on deviantART