The study clarified just how much such an expectation colored their experiences. The subjects were not told which kind of chip they were eating. When the results were tabulated, the people who ate full-fat potato chips had more nausea and comparable gas and bloating than those eating the olestra chips. Preconceived notions certainly colored their observations. Eyelids may twitch, noses may itch, stomachs may growl, knees may pop, ears may ring, or we may sneeze or have momentary lightheadedness.
Similar issues come up regarding the use of medicines.
If a patient was led to expect that a certain medicine will produce a certain side effect, they are much more likely to notice and report that effect. Possible, though rather unlikely. Observing benefit from medicines is also part of the same process. If we expect a certain benefit from a medicine or an herb, we take note of every little minuscule improvement. Only months later will it become clear whether or not we have really improved.