Brady Barr's job often puts him in the jaws of a dilemma.
Barr, who has a Ph.D. in biology, has been bitten by a large boa constrictor, charged by an angry crocodile and faced down a hippopotamus.
The first person known to have captured and studied all 23 species of crocodilians in the wild, Barr will continue his adventures Saturday on the National Geographic Channel's "Dangerous Encounters: Instant Death."
In the program, Barr studies how ambush predators function the way they do.
Ambush predators generally sit motionless and wait for prey to come within striking distance. Their ability to attack in fractions of a second impresses even someone with Barr's background.
"It's just something that you don't normally see," he said today on "Good Morning America." "I'm terrified, I'm not stupid. I know what these animals are capable of."
Among the deadliest of those creatures are crocodiles, snakes, cheetahs and the slingjaw wrasse fish. They attack with such speed that most prey never see the approaching attack.
Barr will induce attacks by some of the world's deadliest creatures.
He'll then film their strikes, then slow down the video to minutely examine their actions and figure out exactly why they are able to kill with such incredible speed that most prey don't see them coming.
"I'm fascinated" by their speed, Barr said. "At the end of the day … I'm afraid. These animals are capable of amazing feats."
Barr found that it takes about one-fifth of a second for camouflage predators to strike.
Boa constrictors, which can weigh up to 100 pounds, poise their bodies like a spring, achieving maximum effect when they attack. The rattlesnake's attack was so fast that Barr had to slow down his video to see the snake had struck, recoiled and struck again in the blink of an eye.
"The day I stop being afraid," Barr said, "is the day I need to find a new line of work."
"Dangerous Encounters: Instant Death" premieres this Saturday, Oct. 24 on the National Geographic Channel. CLICK HERE for more information.