Rat was a comic strip created by Stephan Pastis in his law school years. It essentially served as an outlet for Pastis's thoughts and ideas when he was bored in class. It featured a character named Rat who was rather depressed and philosophical, often musing on life, its complexities, and its possibilities.
Later, when Pastis wanted to become a cartoonist, he added a second character, Poe (the blob o' nothing), who served as Rat's companion. He had completed 30 of these strips and had sent them out to several syndicates, but was consistently rejected as the strip was apparently too dark and depressing.
After this, the character Rat was placed in Bradbury Road, another strip that Pastis tried to get syndicated, but was also rejected.
Eventually, Pastis decided to resurrect Rat with a less depressing tone and replaced Poe with Pig, thus creating Pearls Before Swine.
Most of these strips have never been released publicly, but some of the college strips as well as two of the 30 strips sent in for syndication were included in the introduction to Sgt Piggy's Lonely Hearts Club Comic.