Aha! Thank you!

I definitely should have looked at Symbol.pm before using it in my examples... Now I see why they suggest that you use it (and why the IO modules use it).

So taking into account that Symbol::gensym uses deliberate voodoo, going back to the STDIN example makes it more clear... It is in fact part of the *foo{THING} syntax (*foo{HASH} in these examples):

  DB<13> ${*STDIN}{goo} = 'ber'

  DB<14> x \%{*STDIN}
0  HASH(0x9a7d878)
   'goo' => 'ber'
*  DB<15> x \%STDIN
0  HASH(0x9a7d878)
   'goo' => 'ber'
*  DB<17> x *STDIN
0  *main::STDIN
*  DB<18> x *STDIN{HASH}
0  HASH(0x9a7d878)
   'goo' => 'ber'
*  DB<19> x *STDIN{IO}
0  IO::Handle=IO(0x97a5980)
[download]

And a full example demonstrating gensym's symbol table manipulation:

*  DB<6> $s = \*Symbol::GEN1
  DB<7> x $s
0  GLOB(0x9cca740)
   -> *Symbol::GEN1
  DB<8> x ${*$s}{goo} = 'ber'
0  'ber'
*  DB<9> x \%{*$s}
0  HASH(0x9d4ace8)
   'goo' => 'ber'
*  DB<10> x \%Symbol::GEN1
0  HASH(0x9d4ace8)
   'goo' => 'ber'
*  DB<13> x *Symbol::GEN1{HASH}
0  HASH(0x9d4ace8)
   'goo' => 'ber'
*  DB<15> x *Symbol::GEN1{HASH}{pea} = 'nut'
0  'nut'
  DB<16> x \%{*$s}
0  HASH(0x9d4ace8)
   'goo' => 'ber'
   'pea' => 'nut'
*  DB<17> delete $Symbol::{GEN1}
  DB<18> x \%{*$s}
0  HASH(0x9d4ace8)
   'goo' => 'ber'
   'pea' => 'nut'
*  DB<19> x *Symbol::GEN1{HASH}
0  undef
  DB<20> x \%{*$s}
0  HASH(0x9d4ace8)
   'goo' => 'ber'
   'pea' => 'nut'
[download]

So while there's definitely some black magic happening there (and with the symbol tables in general) I have a better idea of what is happening behind the curtain in this particular instance... I now see where that hash is going (or where it has been (or something like that)). Thank you very much!