Rabbit blowing a horn. Among the marginal creatures populating medieval manuscripts musical animals are fairly common.
This is beyond bizarre - from the Luttrell Psalter, anonymous medieval manuscript known for its scenes of daily life and otherworldly beings.
Royal 10 E IV, f. 3, Mermaid and merman
Prayer roll, MS G.39 fol. 11r - Images from Medieval and Renaissance Manuscripts - The Morgan Library & Museum
Detail from The Luttrell Psalter, British Library Add MS 42130 (medieval manuscript,1325-1340), f171v
Detail from The Luttrell Psalter, British Library Add MS 42130 (medieval manuscript,1325-1340), f172r
Cat with a zither, from a Belgian Book of Hours, c. 1470.
Geoffrey Chaucer, The Canterbury Tales, 14th century ~ British Library #illumination
Calling All Manuscript Sleuths: The Macclesfield Alphabet Book - Medieval manuscripts blog
Book of Hours, Use of Carmel, f.66v (157 x 110 mm), ca.1511, Alexander Turnbull Library, MSR-11