"What the true proverb says has happened to them: 'The dog returns to its own vomit, and the sow, after washing herself, returns to wallow in the mire.'" - 2 Peter 2:22
This verse conjures up a very specific memory from my childhood when my brother and I were dragged to a house of a family friend. We were bored to tears and thrilled when my parents finally decided to leave. We went ahead of them outside and they stayed at the door and talked another twenty minutes or so.
I vividly remember standing outside of the fence of their yard and watching their dog poop and run off, then wait a minute and in wandering around the yard stumble upon his own feces as if a doggie treat. He smelled it for a minute and then ate it. My brother and I were horrified but fascinated. It then threw up and wandered off again, coming back to smell it and then proceed to eat it. This time it didn't even wander off but tried to eat it again.
Over and over again it returned to it's own vomit. I didn't hear this verse or understand it until years later but it has always resonated with me because I've actually been mortified by seeing a dog do this.
And yet we're the same with our sin. Even worse seems to be the people who taste Christ and then leave and return to a life of sin. 2 Peter compares this to returning to vomit.
Our lives of sin. Vomit. Don't keep going back.
p.s. My commentary tells me that in the Old Testament pigs and dogs were the epitome of dirty.