Weird things you find in medieval manuscripts.

Avast Ye Killer Egg!

This image is from L'estoire de Merlin, France ca. 1316; BL, Add 10292, fol. 213r. It shows a mounted knight doing something, jousting, poking, prodding, or whatever, an egg shaped... Horse? Yet another example of "I don't know what the artist was thinking". 

It could just be poor artistry skills. A lake of perspective drawing ability. Or, perhaps, the artist was trying to convey something more sinister.