J. Mann et al., “Why Do Dolphins Carry Sponges?” PLoS ONE 3 (2008): e3868; M. Krutzen et al., “Cultural Transmission of Tool Use in Bottlenose Dolphins,” PNAS 102 (2005): 8939; M. Möglich and G. Alpert, “Stone Dropping by Conomyrma bicolor (Hymenoptera: Formicidae): A New Technique of Interference Competition,” Behav Ecology and Sociobiology 2 (1979): 105.