remember
Explanation
This comic shows a couple in an intimate moment. The man says "I love you Sally" and "And I love you Theodore." But then the woman adds: "I just wish there were some way, some device to make sure I remember this night forever."
In the next panels, the scene is dramatically interrupted by "SECRETARY! GIANT SCANNING SPOTTERS COMING OUT OF THE WALLS!" and "WHAT IN GOD?" followed by "And now you will never forget" with the suggestion that some kind of mechanical memory-preservation device has activated.
The humor comes from the dramatic tonal whiplash. What begins as a tender romantic scene -- two people expressing love and wishing they could preserve the memory forever -- is violently interrupted by a literal, horrifying interpretation of that wish. Instead of the expected romantic response (like "me too" or a kiss), the comic delivers a science-fiction nightmare where enormous mechanical devices burst out of the walls to forcibly ensure the memory is preserved.
The joke plays on the gap between romantic metaphor and literal interpretation. When someone says "I wish I could remember this forever," they mean it sentimentally. The comic imagines a world where that wish is granted by terrifying, invasive technology -- a recurring SMBC theme of taking poetic or figurative human sentiments and exploring what would happen if they were fulfilled literally. The result is that the moment is indeed unforgettable, but for entirely the wrong reasons.