Strangled Thwack (AUDIO) University of Helsinki Your browser does not support the audio element. Caption Vocal sample -- the 'strangled thwack' scream of the tree hyrax. Credit Hanna Rosti Usage Restrictions None 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.