Here is a following quote from a user named Mehni. This could be the reason why this bug exists.
Quote from: Mehni on March 01, 2018, 10:46:44 AM
Expected behaviour:
Pet and wild cats should hunt small rodents such as rats/squirrels/hares.
What actually happens:
Cats rather starve themselves to death rather than lift a paw. While this is typical cat behaviour if I were to believe Garfield, I do believe this is wrong.
How to verify:
Enable dev mode, Draw Prey Info.
What I believe to be the underlying issue:
// RimWorld.FoodUtility.IsAcceptablePreyFor directly checks for ageTracker.CurLifeStage.bodySizeFactor of predator and prey, rather than multiplies that against the body size.
