A 22-year-old man, who maintains illegally numerous exotic snakes at home (suburbs of Paris), was bitten by one of his Bresilian rattlesnakes, the lance-headed viper Bothrops moojeni, with grade III envenomation. The fibrinogen was less than 0,5 g/L, the prothombin time was 22%, the activated partial thromboplastin time was 94 seconds. The authors discuss the biological and clinical management of this defibrination, due to defibrinogenating proteases (thrombin-like enzymes), present in Bothrops moojeni venom. The patient received 7 vials of an antivenom directed to another crotal, Bothrops lanceolatus. Despite the importance of defibrinogenation, there was only a few clinical evidence of bleeding, according to the literature. The normalization of coagulation studies occured only after day 11. This case-report outlines the danger of the increase of exotic snakes maintained as pet in France and the difficulties to obtain specific antivenoms.