Morays have poor vision and rely mostly on their acute sense of smell, making distinguishing between fingers and held food difficult; numerous divers have lost fingers while attempting hand feedings, so the hand feeding of moray eels has been banned in some locations, including the Great Barrier Reef. The moray's rear-hooked teeth and primitive but strong bite mechanism also makes bites on humans more severe, as the eel cannot release its grip, even in death, and must be manually prised off. While the majority are not believed to be venomous, circumstantial evidence suggests a few species may be. Eels that have eaten certain types of toxic algae, or more frequently that have eaten fish that have eaten some of these algae, can cause ciguatera fish poisoning if eaten. Ciguatera fish poisoning is very dangerous and can kill. (Emirates Park Zoo, Samha, Abu Dhabi, Jan. 2015)