"The Cat in Lewis Carroll's books explains that dogs and cats show their feelings through different behaviors. Dogs growl when upset and wag their tails when happy, which helps people understand their mood. Carroll uses this to highlight how animals communicate their emotions clearly."
He then humorously notes that the Cat behaves opposite to a dog's way: it growls when it's pleased and wags its tail when angry. This odd behavior leads the Cat to conclude that it must be mad, illustrating a whimsical and nonsensical view of emotions that fits the playful tone of the story.