Tin foil hat
From Tardis Wiki, the free Doctor Who reference
Tin foil hats were a type of hat which, according to Lucie Miller, were "not a good sign at all". Tom Cardwell wore a tin foil hat. (AUDIO: Blood of the Daleks)
As aluminium was capable of blocking the Bodach's psychic energy, Starkey, Alistair Gryffen and Jorjie Turner made use of tin foil hats to protect themselves. Darius Pike neglected to wear his, allowing the Bodach to send him to sleep and control him into giving up the Eye of Oblivion. (TV: Dream-Eaters)
