Fry makes a crushing discovery; the fossil to his former bestfriend "Seymour" has been found, and the Professor has a way of reviving him through cloning. However, the news about Seymour has Bender upset that he's eventually going to be replaced on Fry's friends list. He gets so upset that he throws the fossil in molten lava. Bender realizes the error of his ways, and attempts to rescue it, which he is successful at. Fry in the end makes the decision not to clone Seymour under the assumption that Seymour has forgotten about him. Fry didn't know that it was the complete opposite.
A magnificent and all around excellent episode. I find that most of these modern animated comedies to be quite funny, though carry within them this dragged out feel that you just want it to end. The episode is rewarded because of the comedy, but it's overall not quite as enjoyable as it should be. This however, eliminates that feeling because of the emotional traits it carries. It starts with the dog itself in Seymour, who displays nothing but love for Fry, as well as simple joys. The ending was such a crushing and depressing blow when Fry decided not to clone his dog, to his ignorance that his dog indeed cared for him his entire life. The ending was really what made it such a great episode.