Ep 20. Stop Or My Dog Will Shoot

In The Simpsons season 18 episode 20, titled "Stop Or My Dog Will Shoot," the beloved family pet Santa's Little Helper becomes a police dog when he assists Chief Wiggum in taking down a criminal during a K-9 unit demonstration. As a result, Skinner offers to train Santa's Little Helper to become a police dog full time, which Homer eventually agrees to after being impressed by the potential financial benefits.

However, as Santa's Little Helper becomes more involved in police work, he begins to lose his friendly and playful personality. His aggression and obedience begin to worry the family, especially Lisa, who becomes convinced that the police force is not a suitable environment for a friendly dog like Santa's Little Helper.

Meanwhile, Bart becomes obsessed with a handheld video game and neglects his schoolwork, causing him to fall behind in his grades. Marge enlists the help of a retired teacher, Ms. Cantwell, to tutor Bart and get him back on track.

As the episode progresses, the two storylines converge when Ms. Cantwell suggests to Bart that they use video games as a learning tool. Bart immediately becomes interested and his grades begin to improve, but Santa's Little Helper becomes even more aggressive and starts attacking people.

In an attempt to resolve the situation, Lisa convinces Chief Wiggum to take Santa's Little Helper off the force and Skinner agrees to find him a more suitable job. After several unsuccessful attempts, Santa's Little Helper eventually becomes a therapy dog, visiting hospitals and bringing joy to patients.

In the end, Bart's grades improve thanks to Ms. Cantwell's unconventional teaching methods, and Santa's Little Helper finds a new calling as a therapy dog, proving that even though things may not always turn out as planned, there's always a way to make the best of any situation.