S4, E4: When Booth's son Parker finds a severed corpse finger in a bird's nest while playing with Booth, the team launches an investigation to find the rest of the body. They locate the corpse in Jefferson Memorial Park, and it soon becomes clear that the death was no accident. With the help of a new middle-aged grad student in the lab (guest star Michael Badalucco), the team identifies the victim as a local veterinarian whose penchant for gambling brings a number of suspects into the picture. When the victim's fatal injuries are found to be from a dog, the team uncovers an illegal dog fighting ring and enlists the help of Cesar Millan to help them connect the forensic canine evidence with the killer dog and its owner. Meanwhile, Booth asks Sweets to psychoanalyze his son who he thinks has been traumatized from finding the finger, and Sweets confronts Hodgins about his attitude in the lab.