Continuity mistake: When Amy is in the kitchen cleaning, she starts mopping the floor, then dancing with the mop held upside down. The mop starts out wet, but when she's dancing it's dry (either that or she would be getting dirty mop water in her face while the mop is being flung around).
Continuity mistake: When Nick is in the spoon, the milk around him turns green.
Continuity mistake: The hole in the window keeps changing size.
Continuity mistake: When Amy walks toward Ron to offer him a truce, her hands are clean, but she somehow transfers mud to his hands when they shake.
Continuity mistake: During the Cheerios scene, there's a shot of a huge green-screened spoon in front of Wayne, coming towards Nick, The spoon's position and movement are totally unrealistic to how Wayne would have moved it.
Continuity mistake: When the neighbour wakes up, the pillow behind him swaps from straight to skewed between angles.
Continuity mistake: When Russ falls off the ant, the grass he lands on bounces up revealing the crash mat underneath.
Continuity mistake: When the kids open the waste bag, Nick steps forward, in between two kids, with about 10 centimeters between each. When the angle changes to Amy, Nick is jammed between the kids.
Continuity mistake: After all the kids have been shrunk, the nail on the floor swaps from laying between two planks to just one.
Continuity mistake: When the four kids run and hide from the ant after he takes over their cookie, Amy has no cream filling on her mouth, but when she tells Ron to be quiet, there is cream on her bottom lip.
Continuity mistake: When the kids exit the waste bag, from the wide angle it swaps from black to light grey. Also, the fence disappears.
Continuity mistake: After Nick falls on the pollen, there's a shot of his mom calling him. Right after, the amount of pollen on him is completely different.
Continuity mistake: When the kids are about to climb the grass, Wayne lets Quark out and the door closes twice: In the close-up and afterwards in the wide angle.
Continuity mistake: Pair of blue jeans disappear from Wayne's shoulder after he turns the faucet off.
Continuity mistake: Nick falls on the pollen on the left side of the flower. When the angle changes he's right on the middle of it.
Continuity mistake: The position of the trash bag left by Wayne differs between shots.
Continuity mistake: When Wayne is destroying the machine, the kids' position differs between the front and back angles.
Continuity mistake: When Wayne tries to shrink the apple, the way he holds the remote control differs between the close-ups and wide angles.
Continuity mistake: When the movie starts and the dog has left the letters, watch the bottles of paint in front of him: They appear closer together in the opposite angle.
Continuity mistake: From Nick's POV, he enters his father's lab and opens the door wide, yet from the opposite angle it is slightly open.
Answer: More along the lines of a serious health problem related to her "plumbing".