"Holey, moley! 8 balls of fur!"
Sounds like something Beaker would say, (if he could talk!) But, yes, to the tune of "Great balls of fire!", this little ditty is called "Holey, moley! 8 balls of fur!" and is extreemly cute! If you want to see it, they recently showed it on episode #4086 - (the one where big bird asks Alan to bake some bird seed cookies for his Granny bird, who is comming to visit.) It is sung, solo, by Little Crissy, and shows 8 different colored fur balls with legs, dancing like crazy, while he sings and plays a piano, ( which ends up falling to pieces in the end from being played so hard!) If you watch that episode you will also be lucky enough to see an ancient clip called "The King of 8".
As for Slimey's trip to the moon, I don't know what season it was from, but I do think that #3726 showed his ship on its way to the moon at the end. You may try to find episodes before and after that number, and try to find which season they were shown in. Good luck!