Hm, strange.. I actually wrote $foo[$[] in the assuption this would prevent any $[-fiddling and force the real solution, but it seems $[ really doesn't work properly in perl: perl -le '$[ = -1; @x = (42); $y = 0; print $x[$y]' prints 42 for me on 5.8.3 and 5.8.4...

I'll add a note to the exercise that the intention is to solve it without diddling $[