answer:Art evolution is not uncommon in animation, and can be caused by a wide range of things, like a change in the staff or the budget, or how much coffee somebody had that morning. The placement of the grill is most likely due to either inattention or else is a response to a dramatic necessity. TvTropes states that, “season one [of Spongebob Squarepants] looks very different from the rest of the seasons. It is the only season that used hand-painted animation cels (beginning with season 2, the series switched to digital ink-and-paint), and the animation is noticeably more crude and inconsistent. Also, Patrick’s appearance is slightly different.”