Why did Ivan Pavlov use a metronome or buzzer in his dog experiments?

Ivan Pavlov used a metronome or buzzer in his experiments to serve as a conditional stimulus.1

In his systematic study of associative learning, Pavlov sought to understand how animals learn by observing their responses to specific environmental cues. He discovered that while food naturally elicits salivation—acting as an unconditional stimulus—other neutral sounds could also trigger this response if they were consistently paired with the delivery of food.1

By using an arbitrary stimulus like the ticking of a metronome or a buzzer to signal the arrival of meat powder, Pavlov was able to train the dog to associate that sound with the upcoming meal. After several trials, the sound alone became sufficient to elicit salivation, demonstrating the formation of a conditioned reflex. This methodology allowed Pavlov to move beyond studying digestion and instead conduct an objective, scientific analysis of how conditioning influences behavior.123