I have given up trying to predict when the rat is going to die. One moment he looks like he won't last the night, and an hour later he's issuing credible threats of mutiny because I took the jar lid away while there were still a few molecules of Nutella left on it. He does still agitate for food, which is an important vital sign for rats on a par with breathing and locomotion, so he's not finished yet.
The back end of the rodent isn't working so well anymore. This isn't a good sign, although it's not an especially bad one either; a lot of male rats have issues with the rear chassis, especially if they're the kind of indiscriminately-bred pet shop snake food whose family tree doesn't fork. It's not dissimilar to the hip dysplasia problem that plagues overbred dogs like golden retrievers. It's a death sentence in the wild, but in captivity it mostly means I get to re-set their cage with a lot of ramps instead of ladders. He's obviously not completely incapacitated, as I can leave him on the bottom shelf of the cage and come back to find he's shoved both other rats out of the topmost hammock, but there's no sense in making his life unduly difficult.
It's also giving him a bit of trouble with eating, as rats normally sit back on their haunches to nom, so that they can use their front paws to cram things into their little faces with maximum efficiency. The lack of traction is also making him not-great at shoving his brothers out of the food bowl, so I've been giving the broken rat personal feedings of calorie-dense nutritional substances, i.e., baby food, which turns out to not be that expensive when you're not feeding an entire baby with it.
It is slightly more difficult than you'd imagine. Adult male rats have an almost religious devotion to being lazy fuckers. The other two have figured out what's going on and gone, "No chewing? Holy shit, sign me up!" They are in absolutely no need of extra calories -- they both squash in all directions already -- so I've been trying my best to at least not give them a lot of the broken rat's extra meals.
It sometimes works to drag the broken rat out of the cage and plop him on my lap for feeding. Sometimes not. It's about 50/50 whether he shoves his face into the jar or just wants to grope his way up my boobs and go spelunking in my sweater instead. It's fine by me if he wants to sleep in there, but I'm not sticking a spoonful of liquefied chicken-and-stars-meal down my shirt. Feeding a rat is not all that unlike feeding a human infant. ("How the hell did you get that on your tail? It is at the OPPOSITE END OF YOU.")
It's also possible to pull the other two rats out of the cage while I feed the broken one. I just pick anything even remotely chewable up off of the floor and let them run around -- my bedroom floor is varnished wood, so I can just sweep and wipe up any rat detritus they leave behind. This only works for a little while. The problem is that all of them know the magical incantation upmommyUP!, whose casting gesture is a constant yanking on my pant leg that transforms almost accidentally into climbing if I ignore them long enough. It's perfectly possible to detach them and deposit them back on the floor, but they just consider that a 'continue from checkpoint'. Unattended, they will in fact keep it up until they reach my shoulder, and then climb down my arm to (try to) stand right on the feeding spoon. The zombie hordes have nothing on the mindless determination of a rat who loves you and wants to know what you're doing.
I've achieved a reasonable amount of success by just giving them what they want in the most obnoxious possible way. I stick the spoon into the cage, encourage the broken rat to snork up as much as he can, and when one of the others tries to grab it, I dump the rest of the spoonful right on the interloper's head and start over again. It takes them a few seconds to go from FUCK I'M STICKY to FUCK I'M DELICIOUS, and then they have to scuttle off and wash the strained peas off their pointy little faces.
Sometimes I can get away with feeding the broken rat an extra helping of something he can eat while leaning on his fat little elbows, but this varies rather widely, especially since one of the other rats seems to think that garbanzo beans are secretly made of crack. David left a jar of dried ones at the back of a shelf of ancient Passover foodstuffs when he moved out. I couldn't immediately figure out if they were chickpeans or soy beans, or if they were still any good, so of course the first thing I did was offer a handful to the rats. (Rats are surprisingly good at identifying and refusing anything that's actually gone off, as opposed to just being bruised or soggy or stale. They don't have the ability to vomit, so they have to discriminate before they wolf it down. Notably, fruit that has fermented apparently counts as a bonus rather than a warning, and a lot of the urban-wild ones have bred themselves into a super-coagulating state where they think the Warfarin used in poisoned bait is delicious.) Two rats went 'yeah, they're okay' and took one each to investigate, but the third rat shoved so many into his mouth he had to use a paw to hold them in place, and waddled as fast as he could get three legs to carry him into the farthest corner he could find to binge on them.