What drives someone to share news stories online? Prior research has identified some possible factors: qualities of the newsconsumer, the news stories themselves and the news consumption environment. We explore an additional factor: cognitivefluency. Cognitive fluency, the ease with which a user reads and comprehends headlines, predicts the rate of sharing ofnews stories. We quantify over 100,000 stories from major news outlets from 2017 and use a bespoke rate-of-sharingmetric, determined by the rate a story was shared on Twitter shortly after appearing on an outlets RSS feed. Cognitivefluency was expressed in cognitive processing (English Lexicon Project). The effect of cognitive fluency is detectable butsmall, and may vary across news outlets. This suggests fluency may serve as a gating mechanism to the propagation ofnews online. We discuss the theoretical implications of this relationship: cognitive constraints of consumers, the structureof the news ecosystem and relationships between these levels of analysis.