I've now transcribed the lyrics from the Muppet Show YouTube video I mentioned above; this variant is clearly related to the second version in the DigiTrad rather than the first, with some distinct alterations -- notably, "Freddie Wilson" has become "Benny" and Rowlf's "human cannonball" verse seems at least partly new.

I've left one word in the second verse in brackets, because I can't decide if it's supposed to be "schlocky", "sloppy", or some bizarre fusion of the two.

THE CAT CAME BACK
performed by Rowlf; The Muppet Show (episode #523)

Little Benny had a cat that they wouldn't let him keep;
So he put her up for sale at a price he thought was cheap.
He took her to a neighbor, to ask him for advice:
He said "Leave the kitty here; she'll help me with the mice!"

REFRAIN:
...But the cat came back, she wouldn't stay away;
She was sitting on the porch on the very next day.
The cat came back; she didn't want to roam,
The very next day it was home, sweet home.

Then Benny met a man who was driving way out West;
He would give the cat a ride as a special honored guest.
The steering wheel was [schlocky?]; he drove into a tree,
The car was just a total wreck as anyone could see....

REFRAIN

Benny bought a gun from the human cannonball,
He put the cat inside with tri-nitro-toluol.
When Benny pulled the trigger, the cannon made a roar;
The neighbors all surrendered 'cause they thought it was a war....

REFRAIN

Then Benny gave the cat to a man who had a bomb;
He took the cat away; she was acting cool and calm.
And then the bomb exploded, it made an awful sound;
They looked and looked for ages and the man was never found....

REFRAIN