What is required for creating a mixed metaphor?

Creating a mixed metaphor involves blending different metaphoric ideas or images in a way that does not align or match logically, resulting in a confusing or humorous effect. This is characteristic of mixed metaphors, as they typically juxtapose disparate elements that do not naturally connect, leading to an unintended or illogical outcome. For example, saying "the wheels are spinning but the engine is running on empty" combines two metaphors from different contexts, which can confuse the listener or reader about the intended meaning.

The other options focus on aspects of metaphor usage that either require cohesiveness or clarity. Hence, while they pertain to constructing metaphors, they do not accurately capture the essential nature of a mixed metaphor which thrives on the incongruity of its combined images.