My Taffy drops balls into the bathtub to watch them roll around against the tub walls. Jumps into the tub to retreive the ball once it stops moving, jumps out of the tub, and starts the process all over again. This can go on for 1/2 hour or more.
She also likes to drop the ball from the top of the steps (per a couple of the videos), but she watches it go down, then fetches and returns to the top of the steps. Retrieving balls from under water in the toilet was a favorite game until all toilet seats in the house were left down (my wife couldn't train me, but...
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Tuck will fetch a ball once. Second throw and he shoots a glare with a "I just got that for you, you idiot!" expression on his face.