Reminds me of Tie::Hash::Cannabinol:

  Tie::Hash::Cannabinol is a completely useless demonstration of how to use Tie::StdHash to 
  pervert the behaviour of Perl hashes. Once a hash has been tied to Tie::Hash::Cannabinol, 
  there is a 25% chance that it will forget anything that you tell it immediately and a 
  further 25% chance that it won't be able to retrieve any information you ask it for. Any 
  information that it does return will be pulled at random from its keys.
  
  Oh, and the return value from exists isn't to be trusted either :)