There is a bug with a specific cat collar which results in some pretty funky graphical glitches to the cat's fur. In Brindleton Bay go to the Lynx household. If the cat called Doc looks stripy/pixellated/shiny then you are affected by this bug:
This appears to affect retina Macs only (I have tested on my retina and non-retina to confirm). There are two ways to work around this issue until EA fix it:
Method 1 - Open the cheat console, enable cheats (type in testingcheats true and hit enter), Shift + click on the cat and select Modify in CAS. Change the cat's collar.
Method 2 - If you want to keep the same collar on the cat, open CAS as explained in method 1 then close it again. You don't have to do anything and the cat should appear normal once again in game. You will need to do this every time you load the game as it is only temporary.
You may also notice that the collar produces a glitch in the fur texture on the hind leg in CAS: