Cavity is a shy fox that literally has a cavity in her left main tooth. You can mainly see it when she opens her mouth. She also has dentophobia, which means "fear of dentists". She probably got her cavity from eating too much candy and that she forgot to brush that tooth. The color of Cavity's cavity is yellow.
Cavity's favorite candy are chocolate Bon-Bons. In a lot of appearences you can see her eating candy. Sometimes her cavity is a deeper yellow then previous episodes. Surprisingly, she doesn't wear candy all over her body, like Nutty. The candy that she eats sometimes varies on the title of the episodes she's in. She doesn't have a lazy eye either.
Cavity's favorite color is purple. This statement is supported by the purple beret that she wears on her head. Another statement is supported that she likes art. Yet another statement is supported is that she was born in France, but moved to the Happy Tree World.
There are many reasons to support why Nutty and Cavity love each other. One reason is that they both like candy. Another reason is that they both have sugar rushes when they eat too much candy.
It is currently unknown how Nutty and Cavity even met.