First off, did you know that not every animal has testicles that descend from their body? Sometimes, those things stay inside and hidden, and you have to go rootin' around looking for them like a pig with a prize truffle.
|Testicle, truffle, whatever.
Hippo testicles are extra hard to find because hippo testicles live in a wibbly-wobbly timey-whimey world where up is down and "staying in one spot" is gauche. So locating the treacherous hippo testicle requires finesse prior to an excavation: you have to use an ultrasound beforehand and often during, and have the leg at just the right angle or the testicles will just... slip all over the place, we guess? Don't worry, we have a hippo leg placement picture for you.
|Please note the standard error bars in location on picture C... and the fact that testicle depth can vary "in excess of 40 cm".
Of course, there's more than one way to castrate a giant animal. Sometimes physical castration isn't the easiest/safest course of action (some animals get troublingly tetchy when their testes are touched). When dealing with a big dangerous animal, it's a lot easier to shoot the animals with fertility-suppressing hormones: no muss, no fuss, no accidental low dosages of anesthesia and sudden unexpected goring! Naturally, this is safest/awesomest from a helicopter.
|The Sarah Palin-approved approach to birth control!
If you want to know more, we highly recommend you listen to the "Never Forget" episode at Science Sort Of, which is an awesome podcast you should know about.
|Elephant control campaign ad?
But don't worry guys, we're not done yet: there's more than just two ways to castrate an animal!
Option #3 is to just damage the testicles so much that they can't recover (sort of the repeated nut-shot version of castration). Just mash them about in the sac a bit, works wonders. This is the method that Laplanders have chosen for birth control with their herds of reindeer but of course, there's always a twist: the reindeer herder castrates their animal WITH THEIR TEETH.
|Suddenly this single takes on a whole new meaning.
FAIR WARNING: this video is so horrible it's like if you took the Tapir Penis Video + the Echidna Penis Video and then watched some dude MAUL THEM WITH THEIR TEETH.
Side note: elephants jerk it with their trunks. Of course they do.
Walzer, C., Petit, T., Stalder, G. L., Horowitz, I., Saragusty, J., & Hermes, R. (2013). Surgical castration of the male common hippopotamus (< i> Hippopotamus amphibius</i>). Theriogenology.