The amount of ice cream in J.D.'s cone changes from one shot to another just after Elliot is caught kissing by Carla.
During the inquest, the sandwich that Kelso takes from Ted is made of a different bread type/shape then the one Ted was holding in the scene prior.
An MRI is constantly on. As soon as anything ferromagnetic comes within its range, which is several feet, it will be pulled in by the magnetic field which is why all bracelets, watches, and other ferromagnetic objects are not allowed in the same room as an MRI.
When J.D. is kicked through the window of Mr. Sutton's house, the window breaks before J.D. goes through it