perl -Mstrict -le 'no strict "refs";use vars qw($x $xr $y);
    $x = 8;$xr = "x"; $y = $$xr; print $y;'
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This works because you can only use symbolic references where the variables are visible in the package symbol table; lexical ( i.e. my() ) variables are not (as you can confirm with the Perl debugger).

Camel 3rd Ed. Ch. 8 refers*

*Sorry