I think that the baby has gone long enough without food, and that forcing is now in order.
Although you recommend mouse tails, I've never used them for the simple reason that they dontt provide a completely balanced meal. I've used forcing for several babies, and always done it with the smallest pinkie mice I could obtain (newborns). I use a fingernail to gently prise the jaws partially open, then insert the nose of the pinkie. From that point, it is simply a matter of gradually working the pinkie back in the throat, until it is about half-swallowed. At that point, I partially release the snakie, to see whether it will finish the swallowing of its own accord. If it makes to spit it out, then I just continue with the forcing until the entire pinkie is within the snakie's mouth. I hold gently the jaws against the pinkie's bottom (the snakie's teeth curve backwards, so this prevents spitting out), until the snakie swallows. Occasionally, it may be necessary to massage the pinkie partly down the neck, but usually not.
Once the pinkie is past the back of the throat, the snakie almost invariably continues ingesting. At this point, I immediately release the baby into its house.
With babies that continue to refuse to feed voluntarily, even after having been forced a couple of times, I continue forcing them for a few weeks to build up their size a bit. Then, I place them into brumation for at least five weeks. After emerging from their "winter" sleep, they almost always will begin to feed voluntarily. In fact, I've only ever had one that didn't do so. He's now over a year old, and still being forced. Hopefully, he'll feed on his own following his second brumation.
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tricia