The third Die Hard movie, Die Hard with a Vengeance, challenged John McClane’s (Bruce Willis) logical skills with a nerve-wracking water jug puzzle, but it can be easily solved with a clear strategy and a little patience. Simon Gruber (Jeremy Irons) tests McClane and his new ally Zeus Carver (Samuel L. Jackson) in a battle of wits through a twisted version of ‘Simon Says’ in which any wrong answer could cause a bomb to explode. Masquerading his plan to steal gold from the Federal Reserve Bank as payback for his brother Hans Gruber’s (Alan Rickan) death, the first test is a linguistic riddle disguised as a math problem, which they fail to solve. However, Gruber tells them the tests matter only when he says “Simon says” beforehand. They fail to deactivate the next bomb, but McClane manages to throw it away at the last second.
With the stakes raised, Zeus and McClane have no other chance but to get the next riddle right. So, after one of the most iconic moments in the Die Hard franchise where the desperate duo drives through Central Park, the second puzzle starts with a simple riddle: “What has four legs and is always ready to travel?”. Zeus quickly identifies it as a joke about elephants (they have four legs and a trunk), and the answer leads them to a fountain decorated with an elephant statue. They spot a suitcase and open it, causing it to activate. Simon calls to tell them that the puzzle consists of filling up a water jug with exactly four gallons of water and weighing it on the suitcase. If time runs out or the measurement is off even by one ounce, the bomb goes off.
There are two jugs available to them: a three-gallon one and a five-gallon one. John McClane first suggests using the three-gallon jug to fill up the five-gallon jug and eyeballing the remaining gallon, but they would run the risk of missing the precise mark. So, to guarantee the maximum level of precision, these are the steps they must take:
- First, they need to fill up the five-gallon jug to the top.
- Out of those five gallons, they need to pour three into the other jug, filling it up.
- Now that the remaining two gallons in the five-gallon jug are exact, they need to empty out the three-gallon jug and pour those 2 gallons into it.
- Then they must completely fill up the five-gallon jug again.
- Knowing that the three-gallon jug needs exactly one gallon to be completely filled, they can use one gallon from the five-gallon jug to get exactly four.
The trick is to take advantage of the two-gallon difference between the jugs and respect the rules of the puzzle. The first time an exact measurement that isn’t three or five is achieved, it can be used to move the contents around in precise portions without having to take any guesses. The puzzle is purely mathematical in nature, so focusing on the additions and subtractions also helps filter out the rest of the variables.
Simon’s tests in Die Hard with a Vengeance set the film apart from movies with similar plots like Under Siege, and the water jug puzzle stood out above the rest. After the movie’s release, it even got nicknamed the “Die Hard Puzzle“. By breaking it down, though, the only question remaining is whether McClane and Zeus share a superpowered ability to focus under the pressure of a ticking bomb.
