Although the quality of the series has been in decline for years.
SpongeBob SquarePants follows the adventures of the title character – a sea sponge that looks more like a kitchen sponge – and his best friends in the underwater city of The Secret Box”.
In it, Patrick reveals he has a box where he keeps something very important to him but that SpongeBob can’t see, which leads SpongeBob to insist, beg, and try to guess what he’s keeping in the mysterious box. SpongeBob ends up revealing a list of secrets to Patrick but to no success, and so he breaks into his house to take a look into it, but to his surprise, he only finds a piece of string inside the box. Once SpongeBob leaves his house, Patrick reveals that the string opens the secret compartment of the box, where he keeps an “embarrassing picture of SpongeBob at the Christmas party”. Before SpongeBob broke into Patrick’s house, he was lying on his bed, wondering what his friend could be keeping in the box, and it’s in that scene where the writers included an Easter egg related to Fincher’s psychological thriller.
SpongeBob starts to wonder if Patrick could be keeping the world’s only albino jellyfish, or maybe Patrick is “a master jewel thief” and has a lot of diamonds inside the box – or, maybe, his best friend is “a deranged maniac who keeps his victims’ severed heads in a box”, and this is a sneaky but obscure reference to the most infamous moment in David Mills (Brad Pitt) and William Somerset (Morgan Freeman) as they track down a serial killer who uses the seven deadly sins as a motif in his murders. In the third act of the movie, the murderer leads Mills and Somerset to a deserted location where they will find his final two victims. Once there, a box is delivered to them, which Somerset opens and warns Mills to not come close. As this was the murder related to envy and the killer was envious of Mills’ life with his wife Tracy (Gwyneth Paltrow), he killed her and kept her decapitated head in the box, with Mills famously shouting “what’s in the box?!”.
This reference to Se7en in SpongeBob SquarePants is very subtle and will go unnoticed by young viewers, but a more mature audience with a wider film knowledge might easily catch this obscure reference. Luckily for SpongeBob, his best friend is not a “deranged maniac” and he doesn’t keep heads in the box, but he won’t be delighted to learn that Patrick is keeping a very embarrassing photo of him.