Plot hole: There is no possible way for the chubby mayor to be able to get in Flint's lab. There is no side entry, and the space other characters use to get in is too tight for him.
Revealing mistake: When young Flint is showing his class his Spray-On Shoes we see the shoes of the class with their untied laces but when the camera is moving towards Flint from behind the class none of the laces are dangling.