Dasyatids generally do not attack aggressively, or even actively defend themselves. When threatened, their primary reaction is to swim away. However, when they are attacked by predators or stepped on, the barbed stinger in their tail is mechanically whipped up. This attack is normally ineffective against their main predator: sharks.[1] Humans are usually stung in the foot; it is also possible, although less likely, to be stung by brushing against the stinger. Contact with the stinger causes local trauma (from the cut itself), pain and swelling from the venom, and possible infection from parts of the stinger left in the wound. Injuries to humans include, but are not limited to: poisoning, punctures, severed arteries and possible death. Fatal stings, such as that which killed Australian naturalist and television personality Steve Irwin,[2] are extremely rare (as of 1996, worldwide known deaths from stingray barb injuries numbered 17),[3] but can occur if a sting punctures the heart or chest, causing complications due to both the sting's location and the poison in the barbs.