http://lljcwddkoyjq3xxtchl7a4i3ig6wqrg7nfxuzbzj4k4tbnb6pnzq7kid.onion/index.php?title=Animal_cognition&oldid=771
The test compares an animal's response to a stimulus or event on one occasion to its response on a previous occasion. If the second response differs consistently from the first, the animal must have remembered something about the first, unless some other factor such as motivation, sensory sensitivity, or the test stimulus has changed.