While looking at a close review item, this looked rather weird:
So I took a look at it on the question, and it didn't look the same:
Here's the edit page:
Is this a bug?
Nick Craver was testing MathJax performance for an answer to a request for MathJax to be enabled on Stack Overflow. It looks like you stumbled into an edit that inadvertently triggered MathJax to typeset an equation.