Here are some possible meanings depending on the context:
1. Literal command: If someone is holding vegetables or other food items, "Cortalas con el cuchillo" means "Cut them with the knife" as a direct instruction.
2. Idiomatic expression: "Cortalas con el cuchillo" could also be an idiom meaning "to cut someone down to size" or "to humiliate someone", similar to the English phrase "to put someone in their place."
3. Figurative language: It could also be used figuratively to describe someone being very harsh or critical, like "He cut her down with his words."
Without context, it's difficult to determine the precise meaning of the phrase. Please provide more information about the situation and who is speaking.