“This paper is an attempt to bring the field up to a scientific understanding of human facial displays, and to restore continuity with modern views of animal communication,” Fridlund said. “From preschool on, we see smiley faces with the word ‘happy’ written under them. We see sad faces with the word ‘sad’ written under them. That may not be the best way to understand facial expressions. A monkey at the zoo that smiles at you is not necessarily happy — it is giving a ‘submissive threat grimace.’” (Source)