Pluto and the Armadillo.

Mickey and Pluto make a short stopover on a South American flight. Mickey throws Pluto's ball into the jungle, and he chases it but it looks exactly the same as an armadillo that's rolled up into a ball. This, of course, greatly confuses Pluto for a while. But he eventually makes friends with the armadillo. He chases the critter into a cave right behind his ball, and rips the ball apart thinking it's the armadillo, which makes him very sad until the armadillo shows up again.