Medieval cats are surprisingly like modern cats. Not poisonous, not made of fire, only plotting murder in a casual, passive way. For once the weirdness was all the Renaissance. Here is Bartholomaeus Anglicus describing an average 14th century cat:

• led by a straw, and playeth therewith
• maketh a ruthful noise and ghastful, when one proffereth to fight with another
  
• unneth is hurt when he is thrown down off an high place*
• a right heavy beast in age and full sleepy

*this translation was edited in the 1800s, which is the only possible excuse for ‘unneth’

Here is a cat helping a nun. Yes, it has a face like a tiny skull, but some cats do.

[Image:British Library, Stowe MS 17, Folio 34r]