The cat in Chopper's Diary was so smelly that one of the cats lay on its owner's butt and was smoked by the owner. Generally speaking, cats that are so smelly may have a surprised face. This is actually a cleft lip sniffing reaction. . When cats smell a certain smell, they turn into a surprised face within seconds and can't even close their mouths in shock.
Cleft-lip sniffing is a unique animal behavior of turning up the upper lip. It looks like being disgusted, but in fact It's completely the opposite. The cat is not deliberately trying to frighten itself; this is simply a cleft-sniff reaction that allows the cat to smell through its nose.