Emotion contagion refers to the emotional state matching between individuals. Adriaense et al. (2018) used a bias paradigm to quantify emotional valence, which along with emotional arousal, define emotions. They manipulated the positive and negative affective states in the demonstrator ravens, which showed significantly different responses to the two states: behaving pessimism to the negative states and optimism to the positive states. Then the researchers trained another observer raven to observe the demonstrator’s responses first and then present the observer with ambiguous stimuli. The experiment results confirmed the existence of negative emotional contagions in ravens, while the positive emotional contagion remained unclear. Therefore, ravens are capable of discerning the negative emotions in their conspecifics and showing signs of empathy.