It is popularly believed that Pavlov always signalled the food by ringing a bell. However, his writings also record the use of many stimuli, including electric shocks, whistles, metronomes, tuning forks, and a range of visual stimuli. Catania did not believe Pavlov ever actually used a bell in his famous experiments. Littman tentatively attributed the popular imagery to Pavlov’s contemporaries Vladimir Bekhterev and John B. Watson, until Thomas found several references that clearly said Pavlov did, indeed, use a bell.