> > What's the difference between /[]/ and / ?
>
> In that context there shouldn't be any difference

If the source is in utf-8, then ruby 1.8 interpretes [] as a choice
of 4 bytes: [195, 169, 195, 170]

Fix is seen as:
[70, 195, 170, 110, 105, 120]

195 & 170 get replaced with "e", hence Feenix.