Problem

• Cats & dogs can’t learn hunting
• Horses can’t learn racing

Cause

It could also be the same skill modifier bug that made Sims not learn the athletic skill anymore and Vampires learn at insane rates.

Solution

• Use the cheat testingcheatsenabled true and shift-click on the mailbox. Then choose make needs static

Mods that solve the problem

• Overwatch, V41 or newer fixes this issue.

Further Reading

• Sim can’t improve theirs skills / Vampires learn insanely fast
• Sim learn skills insanly fast