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. 2023 Mar 4;26(3):727–754. doi: 10.1007/s10071-023-01762-5

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© The Author(s) 2023

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 3 — Example of differences between characteristic facial cues of emotion in a human and dog (Ekman et al. 2002a; Waller et al. 2013) in equivalent emotional contexts (Correia-Caeiro et al. 2017; Ekman et al. 1994). Fearful facial expressions in humans tend to include eyes wide open (AU5) and lip corners stretched horizontally (AU20) while dog fearful facial expressions tend to include panting (AD126). Happy facial expressions in humans tend to include the wrinkling around the eyes (AU6), while in dog happy facial expressions tend to include wide open mouths (AU27). AD: Action Descriptor, AU: Action Unit, AD126: Panting, AU5: Upper Lid Raise, AU6: Cheek Raise, AU20: Lip Stretch, AU27: Mouth Stretch. Dog images modified from Caeiro et al. (2017); Images by users Pexels and 2,843,603 from Pixabay.com (2021), free for commercial use, and by Sifis Kavroudakis from Youtube.com (2021)