Heads and tails are two sides of the many-sided coin that is emotion. This study explores several sides, including those two:
“Indicators of positive and negative emotions and emotional contagion in pigs,” Inonge Reimert, J. Elizabeth Bolhuis, Bas Kemp, T. Bas Rodenburg, Physiology and Behavior, vol. 109, no. 17 January 2013, pp. 42–50. The authors, at Wageningen University, explain (among several explanations):
“Recently, ear and tail postures have been postulated as useful indicators of positive and negative emotions [30], [31], [32], [33] and [34]. In pigs only little research has been performed on tail postures (e.g., Ref. [35]), and, as far as we know, not on ear postures. We, therefore, investigated whether ear and tail postures could be indicators of positive and negative emotions in pigs.”
(Thanks to investigator Neil Martin for bringing this to our attention.)