Dear Editor,rnIn the past five years, we have developed a behavioral model of empathy for pain in rats [1-5].Experimentally, at least two types of behaviors associated with empathy for pain in rats can be identified, based on the evolutionary notion of the Russian doll model [6].One has been referred to as an observer\'s empathic consolation, which is driven by social interaction with a demonstrator in pain [3, 7-9];the other is referred to as observational contagious pain (OCP or empathic transfer of pain) from a distressed objectto a witnessing subject [1-3, 5].]