sneaky message passing is about finding out-of-band channels for passing data between components.
PYK 2014-04-14: I added an object system to Functional imaging which uses $errorInfo to bind methods to their instances. Perhaps this is a hideous thing to do, but in its first application, at least, it seems harmless enough.
Braintwisters and other pages illustrate the art of rewriting procedures as an alternate way of passing information into the procedure.