De Waal is referring to Dale J. Langford, Sara E. Crager, et al., «Social Modulation of Pain as Evidence for Empathy in Mice», Science, 312, no. 5782 (June 30, 2006): 1967. For an overview, see McGill University, «New Pain Research Shows Mice Capable of Empathy», ScienceDaily, June 30, 2006, http://www.sciencedaily.com/releases/ 2006/06/060630100140.htm