Here's why:
* "Les mots" means "the words" in French.
* "Oncle" means "uncle" in French.
The phrase could be used to refer to:
* Words that sound like an uncle might use: Perhaps words that are familiar, friendly, or perhaps even a bit old-fashioned.
* Words that relate to an uncle: This could be words about family, advice, or a particular uncle's interests.
* A playful way to refer to words in general: A way to make language seem more personal or humorous.
Without more context, it's difficult to know the exact meaning intended by "les mots oncle."