Tractionless Self-Propulsion (IMAGE) University of Bristol Caption Crawling is a well-known mechanism for motion on surfaces, but it is ineffective for fast migration in tissues, where cells have to squeeze through tiny gaps. In contrast, tractionless self-propulsion is very suited for that purpose. Credit A. Loisy, J. Eggers, and T. Liverpool, University of Bristol Usage Restrictions Single use only for use with the press release. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.