Continuity mistake: When Robin Williams puts the flubber into his back pocket to show Sara how it will bounce him back up, you can clearly see a hole in which the flubber escapes. When he falls to the ground and Robin Williams turns over the hole is gone.
Continuity mistake: In the scene in which Prof Brainard and Sarah are fighting the bad guys at the mansion, Sarah has Flubber on her hands. She is slapping Wilson around, and you can clearly see that the person who is slapping Wilson is a dummy.
Continuity mistake: When Robin Williams first flies his car, he throws an apple straight down, but in the next bit, the apple is going diagonally. Is it a magic swerving apple that the Prof. created?
Continuity mistake: In the scene where the Professor and Sara are fighting the bad guys, Will Wheaton's character throws an ashtray at the Professor. Before the ashtray gets to him he sprays his rear end with the liquid flubber from the squirt gun. When he does this he sprays his jacket which at that time is covering his rear. When he jumps and hits the ashtray the ashtray does not hit his jacket but hits his pants. According to the movie flubber in any form needs to come into contact with the object to bounce back.
Continuity mistake: After Phillip falls outside of Sara's window, watch the leaves on the ground. They change positions throughout shots.
Continuity mistake: When the scientist throws the balls out the window, they go diagonally into the sky but then they come back down and hit the men who are standing in the place where they took off from.
Chosen answer: It was rice and he just simply dumped them on the floor because he knew he wouldn't be needing it after the wedding to throw at the bride and groom because the Professor didn't show up.