Emotional contagion – the transfer of emotions between people – is thought to occur automatically. We test the prediction, based on evolutionary psychology, that negative, threat-related emotions transfer more automatically than positive emotions. We introduce a new paradigm for investigating emotional contagion where participants are exposed to videos of faces that morph from neutral to angry or happy expressions. Participants watched these videos under high or low cognitive load. Participants reported more happiness in the happy condition than the anger condition and more anger in the anger condition than the happy condition, supporting our new paradigm. Participants in the happy condition were significantly happier under low compared with high load. Participants were equally angry in high and low load conditions.