I think the issue is rusty nails. Their texture is very porous (excellent habitat for bacteria) and brittle (likely to leave fragment embedded). It isn't that

I think the issue is rusty nails. Their texture is very porous (excellent habitat for bacteria) and brittle (likely to leave fragment embedded). It isn't that iron is pathogenic, but that nails inflict deep wounds, and inject many pathogens from the environment. Needle/cutlery punctures, for example, are not associated with tethanus because they aren't rusty or in close contact with decaying matter.