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Many of these are in W|A already without the need for inputting the full formula; just specify various levels of 'heart curve':

...and the 3D surface is there too:

But the URL gives away the punchline.

The equation in the submitted link gave away the punchline too.

The text for the URL on HN gives it away, but the URL itself does not. Which is why I was able to pleasantly surprise a friend of mine with it.