For those of you who haven't seen this episode, here's a summary from wikipedia:
When Fry takes Bender to a museum exhibit, he is shocked to find a fossilized dog on display, which he recognizes as his pet from the 20th century, Seymour. For three days he protests in front of the museum by dancing to the hustle demanding they give him Seymour's body, which proves successful. Professor Farnsworth then examines Seymour's body, and concludes that, due to his unusually rapid fossilization, a DNA sample can be made to produce a clone, and it would even be possible to recreate Seymour's personality and memory.
Fry begins to prepare for the dog and Bender becomes jealous, especially when Fry refers to Seymour as "my best friend". Just when the professor is ready to clone Seymour, Bender arrives. Angry that Fry will not spend time with him, he grabs the fossil and throws it in a pit of lava, believing that destroying it will restore his friendship with Fry.
Fry is furious at Bender and extremely upset at having lost Seymour. Bender realizes how Fry could love an inferior creature and apologizes for what he did. The professor explains that the fossil may not have instantly melted, as it was made of dolomite, "the mineral that won't cop out when the heat is all about". With this in mind, Bender, claiming to be partly made from dolomite, dives into the lava and recovers the fossil.
The professor begins the cloning process and his computer informs him that Seymour died at the age of 15, meaning he lived for twelve years after Fry was frozen. Fry has a change of heart, and aborts the cloning process, believing that Seymour must have moved on with his life, found a new owner, and forgotten about him, saying "I had Seymour until he was three. That's when I knew him, and that's when I loved him. I'll never forget him. But he forgot me a long time ago." A flashback then shows that in the years that passed after Fry left, Seymour had faithfully obeyed Fry's last command, which was to wait in front of Panucci's Pizza until he returned. Seymour stays there as the years pass and he, the pizzeria, and Mr. Panucci begin to show their age. In the final shot, Seymour lies down and closes his eyes.
This is my favorite serious episode of Futurama... apparently many agree with me since it was an Emmy in 2004.
If you've never had a pet, you really need to get one. This episode is a perfect example of a true companionship. This episode really makes you think of mortality, especially if your pet outlives you. We as humans have much to live for, but a dog only lives for their master.
If you haven't seen this episode, just google it and you can find it. Do yourself a favor.