All of the volunteers were “hallucinogen naive,” so had no idea what psilocybin felt like, and neither they nor their monitors knew in any given session whether they were getting psilocybin or a placebo, and whether that placebo was a sugar pill or any one of half a dozen different psychoactive drugs. In fact the placebo was Ritalin, and as it turned out, the monitors guessed wrong nearly a quarter of the time as to what was in the pill a volunteer had received.
