It's not as exciting as it sounds, but to your average well read person in 13th century France, a Manticore was exactly the same level of real as a Zebra. As modern people, we know whats real and whats folklore, but to someone from 800 years ago who's to say?
A bit more interesting, the word Monster, comes from the same root as Demonstrate. Monsters existed to exemplify morality and to provide a Lie to Children as to why certain things are bad ("If you go too close to the rapids Jenny Greenteeth'll get you!")
The monstrous was seen as part of God's plan, and often was interpreted as God asserting His Power it's been a good few months, I can't remember specifics
The "freakshit" threads we had a while back were pretty funny, cause no matter how weird you were, so long as you could confirm that you'd accepted Jesus (and didn't start talking about he minutiae of doctrine) you'd basically be golden in medieval society