Devin Ryan created a computer program that is valid, and produces identical output, in two completely different languages, PHP and Java.
"You were so preoccupied with whether or not you could," writes one commenter, "you didn't stop to think if you should."
/*
<?php
//*/public class PhpJava { public static void main(String[] args) { System.out.printf("/*%s",
//\u000A\u002F\u002A
class PhpJava {
function main() {
echo(//\u000A\u002A\u002F
"Hello World!");
}}
//\u000A\u002F\u002A
PhpJava::main();
//\u000A\u002A\u002F