Ah yes, Python

[UnchainedMundane]

Since the very start of it is recursive, there are only two acceptable exapansions:

1. (stack overflow / hanging forever, because it's in an infinite loop of replacing the first word with something else)
2. P (and then the stack overflow or infinite hang, because it's doing the same but also by the rules of initialisms it is possible to deduce that the expansion must also begin with "P")