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Chaser Had Giant vocabulary, Giant Fan Base

Dog who knew over 1000 words has died
By Karen B. London PhD, July 2019, Updated June 2021
Chaser: Unlocking the Genius of the Dog Who Knows a Thousand Words

Chaser: Unlocking the Genius of the Dog Who Knows a Thousand Words

The dog community has lost someone special this week. Chaser, the Border Collie who knew over 1000 words, has died at the age of 15. She outlived the man who trained her, John Pilley, who was a Professor Emeritus in Psychology at Wofford College. Pilley began training her at age 75 after receiving the dog as a gift from his wife Sally, and passed away a year ago at the age of 89. Pilley’s training of Chaser revealed that dogs’ language abilities are so much more extensive than previously realized.

The pair achieved fame in 2011 when Pilley and Alliston Reid published a paper detailing what Chaser could do and how she was taught to do it. Their paper demonstrated that she could learn and retain a large number of words, that she could understand that general names for items such as “ball” or “toy” could refer to many objects, that she could understand that a single item could have multiple names, and that she could learn the name of a new object by exclusion (when a new name was presented and only one item in a group of objects was novel to her).

Later work showed that Chaser could distinguish between nouns and actions, showing that she could understand syntax. There were some interesting revelations about what was particularly challenging for her. Pilley found through experimentation that she had trouble understanding the cue “Take ball to Frisbee” but could do as instructed when told “To Frisbee take ball” instead. The crucial factor seemed to be that she acted on the last word she heard.

Pilley had long said that Chaser’s accomplishments are not a result of her being unique or so incredibly intelligent compared to other dogs. He maintained that many other dogs could learn what Chaser did as long as they were taught as Chaser was. She was taught methodically and extensively, sometimes for many hours each day. Pilley felt strongly that play and fun were critical components of successful learning because tension and fear get in the way of learning by inhibiting creativity.


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Pilley was very wise in his education of Chaser, and I think that the process of how he taught her is the most important takeaway from her life—rather than the impressive amount that she did learn. Based on Pilley’s remarks in his 2013 interview with Julie Hecht, we can see that his patience and respect for his dog provide wonderful insights for all of us. For example, he maintains that if a dog is not performing a behavior as requested, that the best thing to do is to assume that he dog does not understand. Pilley urged everyone to discover how smart their dogs are and get to know them. He wanted each of us to find out what makes our dogs happy, giving them opportunities to explore their interests. He believes that better understanding leads to better communication, which leads to more happiness.

Chaser died of old age and was generally healthy right up until the very end. She had been receiving acupuncture treatments because of some arthritis, but was not suffering from any specific illness. She was with family members as she peacefully passed away, and was buried in the backyard along with some of Pilley’s ashes.

You can read more about Chaser in Pilley’s book Chaser: Unlocking the Genius of the Dog Who Knows a Thousand Words and read our review.

Karen B. London, Ph.D. is a Certified Applied Animal Behaviorist and Certified Professional Dog Trainer who specializes in working with dogs with serious behavioral issues, including aggression. Karen writes the animal column for the Arizona Daily Sun and is an Adjunct Professor in the Department of Biological Sciences at Northern Arizona University. She is the author of six books about canine training and behavior, including her most recent, Treat Everyone Like a Dog: How a Dog Trainer’s World View Can Improve Your Life