What is in $\mathbb{I} - \mathbb{N}$

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In the Wikipedia page for the axiom of infinity it states that the natural numbers are a subset of the set that the axiom defines. Then gives a way of extracting the numbers from it. However I'm curious about these non numerical elements of the infinite set. What do they look like and why are they in the set?

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The axiom specifies some things that must be in $\Bbb I$, but does not specify that anything in particular is not in $\Bbb I$. If you take any set $a$, it could be in $\Bbb I$. Then all the sets in an inductive chain starting with $a$ must be in $\Bbb I$.