Kate Hartman's Muttering Hat
Frankly I think this woman looks as uncomfortable as I am at the thought of a hat that constantly mutters to you, giving the impression of either snippets of your internal dialogue being made public or – a little more distressing – hearing voices in your head. Constructed from mp3 players, headphones, speakers, plastic funnels and microphones, and enclosed in a swish felty hat, the art project is designed to give people an insight into "the soundtrack of our own musings."
Designed by Kate Hartman it takes two forms, where either the hat's earmuffs partially block out external noise and replace it with pre-recorded mutterings (you can detach the muffs, as shown in the picture, and share the oddness with friends) or – thanks to a communication built into the hat – you can speak your internal dialogue out loud with it remaining in fact partially covert.
There's a video of it in action here.