We all know Daryl Dixon is a badass, and it seems like the actor who plays him, Norman Reedus, is probably one as well. In the ultimate test, Andrew Lincoln (who plays Rick Grimes) and prankster Nick Santonastasso team up to put Reedus in a "real" zombie attack.
Born with Hanhart syndrome, which causes physical abnormalities including missing limbs, Santonastasso came to internet fame by pulling similar zombie attack pranks in his home state of New Jersey. Between his positive attitude and this Examiner story, which reported how Santonastasso wanted to star as a zombie on TWD and on the internet petition that campaigned for it, the show discovered the young fan, and then flew him to Japan andhad The Walking Dead's special make-up effects artist Greg Nicotero could zombify him appropriately, all so the show's cast and crew could see how Reedus would react when a zombie popped out from under a room service cart.
The answer, as you have probably gleaned from the headline, is "Completely fine." As you can see, Reedus only emits a mild yell of surprise, but very quickly remembers there actually are no such things as zombies, Actually, the actor probably reacted better than Daryl would have, in that Daryl would have immediately shot this zombie attacker in the head with his trusty crossbow, while Reedus failed to murder the zombified Santonastasso. Winners all around, I'd say!