[A British Museum curator] said snails were often depicted in the margins of medieval illuminated manuscripts, thought to symbolise cowardice. That could mean it is “a satirical reference to cowardly or non-chivalric behaviour of opponents in battle, or as a parody of the upper or knightly classes”.
[The curator] said satire was often found in medieval material culture, with one of the most popular visual gags being a monkey, in place of a doctor, examining a flask of urine for its clarity and colour – the go-to method for diagnosing medieval ailments.
That at least is graspable for modern audiences. Less so are the comic intricacies of a male knight wearing a Norman-style helmet, apparently praying, with one leg lunging forward as he steps from a snail on a goat. The museum called it a form of “medieval meme”.