 A chimpanzee attacked and severely injured its keeper in Alipore Zoo, and numerous other incidents have been reported including the case of an elephant trampling its mahout to death in 1963 which had to be put down.In 2001, it was revealed that zoo staff drugged the great Indian one-horned rhinoceros into relieving itself more often than normal, which enabled them to collect the urine and sell it on the black market as an anti-impotence medicine.The zoo attracted flak from the scientific community in general, because of cross breeding experiments between lions and tigers to produce strains like tigons, and "litigon"s (see Panthera hybrid).