As with previous games in the series, Metal Gear Solid V is full of goofy easter eggs. One of them, however, is actually pretty handy.
(Minor Metal Gear Solid V spoilers ahead.)
Steam user Akutare put together a Very Serious Guide for one of MGSV's least serious weapons: the water pistol. It is not — despite what you might think — entirely useless. Akutare notes that it can be used for everything from hold-ups (it's not like guards can tell you're jabbing a fake gun between their vertebrae), noise distractions, stuns, and putting out fires. Nothing too terribly special, but nice to have in a pinch. Now for the good stuff.
Akutare points out two especially interesting uses for the not-even-a-pea shooter. First up, it can detonate mines from a distance. Akutare writes:
"Considering the Magazine is not able to blow up mines, that leaves the Water Pistol to be the only infinite source that can blow up a mine from a distance. Generally it is better to just go around them and pick them up, but still has a use of being ranged mine disposal."
Second, it can disable electronics, and — crucially — it sends them sputtering into the scrap heap silently. Akutare explains:
"Last but definitely not least, is the VERY useful ability to take out electronics silently without the use of explosives. All it takes is one shot before the target starts fizzling and eventually gets destroyed all with much less suspicion than the normally used explosives. This works on Communications Equipment (the Radar Dishes), Radio Transmitters, and the Power Supply giving a very quick and silent way of crippling the enemy."
There are some other, significantly more spoilery ways you can turn the water pistol into a legitimately useful item as well. Check out the full guide if you want to tarnish your virgin eyes with those.