Tooth and Nail is episode 9b of season 3 of Rocko's Modern Life.
Rocko, Heffer, and Filburt go to a Scratch and Sniff Cafe, where they scratch whatever is on the menu and order it by its smell. Rocko reminds Heffer that he has already ate before arriving at the restaurant and tells him that he has an eating problem, which Heffer delusively denies. As a waitress offers the three friends their menus, they scratch their orders in and Rocko tries to scratch his order in and can't. Heffer and Filburt figure out that Rocko has a nail biting addiction. But Rocko denies this, claiming that he has a bad scratching card. As he and Heffer argue over this, Heffer gives Rocko a dime to pick up. Due to his lack of fingernails, Rocko has trouble picking up the dime with his fingers. Despite this, Rocko, still delusional, shouts out that he doesn't have a problem and runs off.
Back at his house, Rocko continues to deny his problem and says that his tendency to bite his nails is nothing compared to Heffer's gluttony or Filburt's neuroticism, which Rocko deems as real problems. He tries to open his can of Root Beer, but his lack of fingernails once again squelches his attempt and he furiously slams the can on the table, spraying himself with the soda. It isn't until Spunky scratches the fleas off his body and the fleas transfer to Rocko's body, prompting Rocko to scratch himself, which he is unable to do, that he finally concedes his nail-biting habit.
As Rocko struggles to control his nail-biting habit, he hears the doorbell ringing and hides his hands inside a monkey puppet and a ham in order to hide his chewed-up fingernails. As he answes the door to find Heffer and Filburt standing there, they ask if Rocko is hiding somehing. Rocko furiously tells them that everyone has something to hide and slams the door shut. Heffer and Filburt realize that Rocko's habit is worse than they thought as they turn to leave. In order to contrive a way to control his habit, Rocko searches through the phone book to find a place that does that and comes across the Chameleon Brothers' Sure Cure Clinic.
As Rocko makes it there, Chuck and Leon escort Rocko out the clinic, saying that it is exclusive. They do, however, offer Rocko a bag, only for the wallaby to discover that the bag is completely empty when he checks inside the bag back at home. Furious that he has been ripped off, Rocko balls the bag up and heaves it to the floor. The bag then reveals a large set of six steps, which animals, known as the 12-steps, emerge from. They help him with his nail-biting habit, getting him to admit it. When the others hear about this, six of them decide to leave to take a trip to Las Vegas. The second step Rocko is given is to squish the fish. Rocko has fish on hs feet used as water skis and sides through a puddle. His third step is to smell the rhinoceros, which crushes him as he does. The fourth step he is given is to shave a weasel. As Rocko gets to the fifth step, which is smell a foot, he becomes annoyed and asks what any of the steps have to do with his habit. This prompts him to come across Death, who introduces his future as the sixth step. Rocko's scenario shows that Heffer and Filburt come across a store named Feet of the Stars and views most of the feet that have been cut off from other citizens. So Heffer and Filburt search for Rocko and finally find him in the dumpster chewing on a foot. The two leave the wallaby to get chili.
Back in reality, it's revealed that Rocko had been dreaming and he is chewing on Heffer's foot. Heffer kicks him off and Rocko lands onto the couch. He finally wakes up and decides to never bite his fingernails again. At they end the other 6 steps are shown gambling in Vegas and losing money, showing that they ironically have an addiction as well.