Mixed metaphors are usually speech mistakes by people, and are very amusing. Here are a few examples.Is there a single word for denoting mixed metaphors?
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I had to go to the reverse dictionary for this one.
From what I understand, a mixed metaphor is an example of a catachresis, but not all catachreses are mixed metaphors. Wikipedia says that "Catachresis is 'misapplication of a word, especially in a mixed metaphor' according to the Penguin Dictionary of Literary Terms and Literary Theory."
Here's Merriam-Webster's definition of the word:
A very good term for this when done deliberately is metalepsis. The OED defines metalepsis as "the rhetorical figure consisting in the metonymical substitution of one word for another which is itself a metonym"; or, more generally, "any metaphorical usage resulting from a series or succession of figurative substitutions." An interesting extended discussion with examples is available here.
@Tragicomic is right that most of the examples on the page you linked seem to involve some aspect of catachresis or other (likely non-deliberate) rhetorical false stepping. In this vein, I would like to also draw your attention to the concept anacoloutha, meaning "[use of] a non-reciprocal synonym"; "a word of meaning similar to a word but that cannot substitute for that word in all uses" (source). This, I believe, is the essential trope underlying the inadvertent mixed metaphors cited by your page.
Whorf's discussion of the ideology of reference and "dialogic processes" gets at the same idea (usually in more general terms, but he offers some very specific examples which are indeed akin to your "mixed metaphors").