Hippety Hopper escapes from a zoo. When Sylvester sees him, he believes that that the kangaroo is actually a king-size mouse. A bulldog tries to convince the cat that there is no such thing, but when he too sees Hippety Hopper and his mother (who was searching for him), he and Sylvester hitch a ride on the Water Wagon.
(1992) LaserDisc - The Golden Age of Looney Tunes: Volume 2, Side 9: Best Supporting Players
The cartoon was reissued in the 1954-55 season (evident from the style opening Color Rings used: red rings with a blue background). Unlike most other reissued Looney Tunes, the original closing sequence was kept. This is one of four pre-1948 Looney Tunes to keep the original closing.
The song playing on the opening titles is "You Never Know Where You're Goin' Till You Get There", which had been sung by Sylvester earlier in "Back Alley Oproar". The same song is played on the opening titles of "Hippety Hopper" the following year.
Coincidentally, all three of the cartoons had their original titles lost due to blue ribbon reissues and later restored with the original titles.