I really like your example, it seems highly believable. One feature that pops up in many scattered spiritual beliefs is that they can often link to observable health effects (... poor wording of my thought). As a rough example:reizoukin wrote:Honestly, I use the already-established culture, habits, stereotypes, setting, etc. and mash them together, or extrapolate. For example, I once thought up a culture which lived on the edge of the lake, and disposed of their dead by dropping the bodies into the lake with a weight to sink them. They came to the belief, over time, that their dead were then reborn as fish, and so the people refused to eat fish. When they first started dropping the bodies into the lake, they didn't have any preconceived notion about it; they simply saw the opportunity to dispose of the bodies in a handy way. Then their imagination kicked in.
So I guess what I'm saying is, give them habits and stereotypes and settings and a bit of culture, and extrapolate on THAT.
If people fall sick more often when they keep their dead in their dwellings for long periods, they might gain the belief that the spirits of the dead get angry from being confined (or any of hundreds of possible explanations) and take that out on the living (making them sick). This could lead to the practice of cremation, to free the spirits of the dead, or leaving them far from the homes of the living. The belief, without foundations in medical understanding, serves a distinct health service in reinforcing some standard of sanitation.
I don't know if it's a useful thought but thinking along those lines can develop a few beliefs and traditions, if you haven't considered it before.