a trick that I learned when mine went off feed for long periods was to offer them electrolytes in their water.... you can get this from most bird shops or tack shops. the electrolytes stimulate their appetites and will keep them very well hydrated if there is another issue going on with the snake.

without food.... i would strongly recommend that you offer a constant supply of water if they are not eating.. I know many breeders and keepers rarely offer their rosys water, but I myself have a kept them for years and never ever had a problem do to them always having a water bowl in their cage.

I would also suggest you get that snake to a vet for a fecal exam... may have a parasite or problem with the gut...

hope it helps.
byron.d