Two Ravens and One Crow (The Iron Druid Chronicles #4.3)

by Kevin Hearne

“What are guilt ferrets?” “They’re bastards. They cling to your neck and tickle and bite and generally make you miserable, which is a pretty good trick for a metaphor.” They were also impervious to logic—perhaps their most diabolical power.

Guilt ferrets is an amazingly useful saying. When you haven't technically done anything wrong, but you still have that creeping suspicion you should feel like you did.