Check the global temp vars, files and caches. Encapsulated scoping is a lie we've been told to help us sleep better at night. Some of those seemingly well defined system functions bleed out to caches for (slight) performance gains.

You could have the most locked down explicitly defined well scoped code in the world, and it just takes one measly baked in call to a global function to shatter that dream house into a thousand pieces.

I'm looking at you string-match; you know what you did.