Endorphins, I presume.
D000349:Africa; D000818:Animals; D004723:Endorphins / Q000502:physiology*; D005197:Famous Persons; D005239:Fear / Q000502:physiology*; D049671:History, 18th Century; D006801:Humans; D008045:Lions; D008297:Male; D010146:Pain / Q000503:physiopathology* / Q000523:psychology; D012606:Scotland; D012684:Sensory Thresholds
D004723:Endorphins