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In a famous experiment, Pavlov taught dogs to associate dinner with the sound of a bell. The dogs would salivate whenever a bell rang regardless of whether food was given to them. This indicates that a dog considers a simple association of events happening closely in time to be necessary.

In the new experiment, the rats were also taught to associate a sound with food. But then, instead of just listening to the sound, they were allowed to provoke the sound themselves. The researchers found that when the rats produced the sound themselves they didn't go to look for food. Thus, it is clear that they understood that food is not necessarily associated with the sound. And if they had caused the sound, it was obvious to them that food would not be available - because they weren't the cause behind the distribution of food.

"When it rains, you expect that both your lawn and your neighbor's lawn will be wet," says Michael Waldmann, an experimental psychologist at the University of G�ttingen, Germany, "but if you water your lawn, you wouldn't expect your neighbor's to also be wet. And this is the type of reasoning the rats are using."