Chuckie loved Melville dearly and confided to him with things he never told anyone. He also played many games with him like fetch, exploring, bugs in the rug, eating chocolate pudding, and even tried to once eat leaves like Melville did. This joy was cut short when Chuckie brought him over to Tommy's house. He asked the others to care for him while he looked for a special type of leaf for Melville. After Chuckie left, Tommy and the twins decided to see how Melville was. However, when they checked, they saw that Melville didn't move. Although Tommy was initially confused as to why, the twins suggested to him that Melville could have been dead, then went on to explain what death meant. (It should be noted that in this episode I Remember Melville this is the first real time the Rugrats talk about, and get an understanding of, death.)
Although Tommy was not sure at first if Melville was indeed dead, Phil did various things, all of which Melville never moved as a response, then said, "Yep, he's dead alright". Although the twins wanted to try and forget what they just learned, Tommy convinced them that they have to try and break the news easily to Chuckie. They even tried to find a new bug to replace Melville and quickly picked a snail. However, Phil stated several times that he didn't see a snail as a bug. When Chuckie saw the snail, he agreed with Phil and demanded to know where Melville was. When they told him that Melville was dead, Chuckie didn't believe he was really dead and tried very desperately to awaken his dead pet. Even after multiple failures, Chuckie still didn't believe Melville was dead and tried to play with the dead bug on a toy circus he had made. But after seeing Melville not even stay on a ball, he broke down crying from the realization that his pet was dead, then declared he would never be happy again. The following day, while the babies tried to be sensitive to how Chuckie reacted to Melville's death, Chuckie appeared to be over it. Believing him, Tommy took him and the twins inside to have chocolate pudding, but no sooner did Chuckie start eating did he begin to cry, remembering how he and Melville had shared chocolate pudding before Melville died. Tommy then decided to put the pudding away and try to find something that won't make Chuckie remember Melville.
Chuckie, however, declined, saying that he wanted to remember him because if he didn't, then who else would? He also said that he still liked chocolate pudding. Tommy, confused, asked why he did to which Chuckie tried to figure out why. He then calmly answered Tommy that he "Never got to say good-bye". So, to give Chuckie some closure, Tommy and the twins gave Melville a funeral and as the twins said some good words and some things they remembered about Melville, they both began to cry. Chuckie then laughed, shocking everybody. When they asked why he was laughing, he happily responded that he was laughing because he was happy and that the memories they reminded of Melville gave him joy. He then said that from then on when he thought of Melville, he would be happy to which both twins cried for no reason much to Chuckie and Tommy's surprise.
Melville died of natural causes.
You can find Melville gallery here.