Evening,
It appears that scratches from non-zombie sources (I.E. moving through trees, brush) carry the infection chance from zombie scratches. I just lost a character in this manner. He was scratched with no zombies around while going through trees/thick brush, got anxious moodlet. Later that evening I messed up burning some corpses, and the corpse reanimated after death.
This may need to be looked into, since only zombie scratches/bites should be zombifying... not scratches from moving through trees...