The power of backspace
If one can pack the source code with backspaces, typically by using an obscure placeholder character and then running a find&replace script to replace the placeholders with ^h, then one can completely separate the apparent source code (which is actually just trailing comment text), from the actual source code (cleverly hidden 'beneath' the backspaces).
Here's a trivial example written in BASIC where 'ĥ' is used to represent the ^h backspaces that have been packed into the code by a trivial script.
10 PRINT "YES!!"; REM ĥĥĥĥĥĥĥĥĥĥĥĥĥ"NO!!"
10 PRINT "NO!!"
With this trick, one can do almost anything. The source code can be whatever you want, because it's just commenting, while the actual code is hidden by the backspaces.
I came up with this evil trick around 1980 or so. A nice example was making LIST appear to do RUN, and make RUN appear to do LIST. Mysterious math errors were fun. Almost no limit.
(I know other languages, but I chose to use BASIC for this example. Forgive me.)
This will probably work with any language that allows trailing comments on a line.