Go to girl, it tells you that it lost its guineapig.
Go to library, find some things out about guineapigs.
1. that they dont like it outside
2. that they like grass (or something else) more than anything else
3. that they like to hide under sofas, carpets, etc...
Go outside to a clearing, get some grass or go to the garden and
dig for vegetables...depends on what you need for the guineapig
Go to cellar, find the guineapig under the carpet 
kill the cat, drop food
Guineapig comes out, if you still have food on you and the book,
 it will follow you
Go back to girl  
quest finished


