Here is a very short video from Seedy, only a minute long, explaining an interesting bug in The Legend of Zelda: Ocarina of Time.
OoT handles fiery environments without the Red Tunic, and being held underwater by wearing Iron Boots without the Blue Tunic, in an unusual away. You might expect them to return Link to the last safe place he had been, like when falling into a void, or else maybe kill him instantly, or at least cause periodic damage. Instead, for whatever reason, the designers chose a unique way to implement the danger Link is in.
While in hot places or stuck underwater without the proper tunic, the game starts a timer, with time relative to the amount of health that Link has. If Link leaves the area or puts on the right tunic before time runs out, the timer goes away and Link takes no damage regardless of how much time was left on it. However, if the timer expires before Link reaches safety, he just dies instantly, “getting a game over” in the clumsy parlance of video games. You’d think it’d be better just to inflict some damage on Link every few seconds, but that’s not how they chose to do it.
Link gets eight seconds on the clock for every full heart he has. Fractions of a heart grant proportional time. While the game only displays health in quarter-hearts, Ocarina of Time actually tracks hearts in 16ths (each full heart is effectively 16 hit points), and each 8th of a heart grants Link one second on the timer.
So, what happens if Link has exactly 1/16th of a heart? The display rounds up, so it looks like Link has a quarter of a heart left, but he’s considerably closer to kicking the bucket than that. He has less health than what’s needed to get a one-second timer. How does the game cope with that?
It does it by just not starting a timer at all! If Link is almost dead, paradoxically, he becomes immune to fire and drowning timers. He’s still in great danger, for any attack on him in this state will kill him immediately, but it makes tunic-less challenge runs a bit more interesting.
Break Timers With Low Health (Youtube, 1 minute)