Both Uses

fester
in
Flags of Our Fathers
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He fell once, dashing to elude gunfire, and reopened his festering wounds.†
Chpt 9. *

festering = (of an injury) getting inflammation and creating pus OR (generally) getting worse -- especially through inattention
Only later would the Marines comprehend just how much danger still festered inside Suribachi on the morning of February 23.†
Chpt 11.

festered = (of an injury) became inflamed and created pus OR (generally) got worse -- especially through inattention

Definitions:

(1) (fester)
to grow worse or more intense over time, especially when ignored; or, in the case of a wound, to become inflamed and filled with pus
(2) (meaning too rare to warrant focus)