This here is my secret box. If I showed you what... - SpongeBob Freeze Frames
Mystery box Surprise
Secret Compartment Box - Revisited - YouTube
Mystery Box! – Sweet As Treats NZ
Spongebob] In the Episode "The Secret Box", The box's secret compartment that is opened by pulling the secret string is foreshadowed earlier when Patrick pulls Spongebob's tongue in his sleep : r/TVDetails