Here I am gong to attempt to gross you all out. That's your warning.
This is what I do at work.
Yesterday someone brings us two adult guinea pigs. Drops them off at the store, they don't want them anymore.
About 5 minutes after being introduced to the other adult guinea pigs in the petter, I heard all kinds of squealing and thumping, the kind that means trouble in Cavy Land. So I go to investigate.
They are all males in this box.. or they SHOULD be (with the boxes open, people tend to pick females up and drop them in the male side, either on purpose or because they aren't paying attention). But two of the males are chattering with their lower jaws quivering, which is usually only something they do when females in estrus are present.
So I start to pick them all up and push on their bellies, which is how you get their little boy bits to pop out and ensure that what you have is, indeed, a male. Something pops out, male. Nothing, female.
I pick up the final guinea pig, one of the new comers, and I push on the little spot.. and instead of just getting what I normally get, I get that and a waltnut-sized mound of poo.
Guinea pig anatomy is a little strange. (Even aside from the fact that it looks shockingly like human anatomy in miniature if you protrude it right.) Both males and females have what look like labial lips normally. They aren't vulvas, really. But their anus is tucked up inside this little pocket.
Apparently this guy had been having trouble with his bowels being softer than normal, and instead of pooping nice, hard little pellets, he had been pooping softer ones that weren't being fully expelled from this little pocket, called the perineal sac. Instead, they just got impacted in there.
It was really bad.
So, while one of my coworker's wrapped the ill-fated little cavy up in a towel and held him, and the other one of my coworkers fully inverted his pernieal sac for me, I had to flush the area out with warm water, peroxide and mineral oil and then set about with a pair of tweezers and get all that mess out. It took about twenty minutes.
Through all this, that poor little animal held perfectly still for us. He didn't scream, he didn't squeal and he didn't so much as twitch, despite the fact that having his junk inverted like that had to be uncomfortable, and the area was probably already very tender because the bacteria in all that mess had just started to create sores on his skin.
I felt so badly for the little guy. And even after we were all done, and I'd go to check on him, I could pick him up with no problem. He held no grudges.
Animals are amazing.
Moral of the story: If you have a male guinea pig, as distateful as it might be, please check his perineal sac to make sure he isn't getting an impaction. His anus was completely blocked when we got to him, and if it had stayed that way much longer he probably would have died.