"Cell yell" isn't the only thing that makes overhearing a
mobile phone call so intrusive. According to University of York
psychologist Andrew Monk, hearing only one side of the
conversation is what really drives us to distraction.
Monk and colleagues found that British Railways
passengers were only mildly disturbed to overhear two people
chatting in the seat behind them. But when only one side of the
conversation was audible (because the other party spoke very
quietly), passengers rated it just as annoying as a cell phone
call. The findings were published in Behaviour &
Hearing only one side of a conversation compels us to pay
extra attention to it, Monk explains. The "need-to-listen"
effect isn't due to morbid curiosity, however. He theorizes
instead that our brains, expecting information to arrive from
both sides of a conversation, have an innate tendency to try to
fill in the blanks—whether we like it or not.