Simon B. N. Thompson,  Saliva Cortisol and Yawning as a Predictor of Neurological Disease.   journal   = {International Journal of Psychological and Behavioral Sciences}, [online]. World Academy of Science, Engineering and Technology.
    March 2016, vol. 112(4). 211 - 214
    [viewed 03 June 2020]. Available from: https://publications.waset.org/pdf/10004285.