Ivan Pavlov was a Russian physiologist whose dog experiments in the late 1800s and early 1900s became the classic example of classical conditioning, where a neutral signal like a bell came to trigger salivation after being paired with food. Online, his name turned into shorthand for any automatic, trained reaction. Clips using the bell or his name circulate in meme edits and reaction videos because the reference is widely taught in school, instantly recognizable, and easy to apply to phones, games, food and everyday habits.