Courts saw a century ago that juries cannot disregard inadmissible evidence

Evidence

In fact, judges and courts were keenly aware of this fact over a hundred years ago. In 1912, using the wonderfully apt analogy that ‘you cannot unring a bell’, the Oregon Supreme Court concluded the following when referring to an improper testimony during an arson trial: ‘While in some cases an express instruction to the jury to disregard testimony injuriously admitted is properly held to cure the error, yet the courts are cautious in the application of this rule. It is not an easy task to unring a bell, nor to remove from the mind an impression once firmly imprinted there …’ Studies with mock jurors have shown that despite clear instructions to do so, inadmissible information is rarely disregarded by the jury when making verdicts. — Sander van der Linden, Foolproof, 252