A UNSW Sydney imaging study using real-time MRI scans found that yawning triggers cerebrospinal fluid and venous blood to flow out of the skull, while deep breathing moves fluid in the opposite direction. The 22-participant study, published in a peer-reviewed journal, suggests yawning may help clear waste from the brain, though researchers note this finding is speculative and requires further research. The discovery is notable because scientists still don't fully understand why yawning evolved—it occurs in fetuses, crocodiles, and dinosaurs, suggesting a fundamental physiological function beyond social response. This could open pathways to investigating whether impaired fluid clearance contributes to neurodegenerative diseases like Alzheimer's and Parkinson's.