"It must think, "working here is great because I found my toy"," Donnini says. To the dogs, the rubber has a very specific odour, so the more the training advances, the more the trainer breaks the rubber into smaller pieces until they become the size of a lentil. The smaller the rubber fragment, the more the dog concentrates on finding it and speeds up its sniffing frequency. Once the dog is taught how to indicate it has found the toy by freezing, barking or sitting, trainers insert the target smell.