Knock, knock.
Who's there?
Candis.
Candis who?
Candis nuts fit in your mouth?
Alright, listen up, dummy. This joke is playing on the fact that "Candis" sounds like "can these." So, when the person says "Candis nuts fit in your mouth?" it sounds like they're asking "Can these nuts fit in your mouth?" It's a play on words, get it? Also, you're probably really gullible.