bedroom-experimentation
Explanation
The Joke
A couple is in bed together. One partner says, "I think we should... experiment more in the bedroom." The other enthusiastically agrees: "Let's do it."
The next panel reads "Later that day..." and one partner walks in to find the other in bed with a third person. Shocked, they exclaim, "What are you doing?!" The partner in bed calmly responds, "Uh, it's called a control group?"
The Humor
The joke hinges on the double meaning of "experiment in the bedroom." The first partner clearly means sexual experimentation -- trying new things to spice up their love life. The second partner takes the word "experiment" literally, in the scientific sense, and sets up a proper controlled experiment by establishing a control group (sleeping with someone else for comparison).
The humor comes from the absurdity of applying rigorous scientific methodology to an intimate situation. In a real experiment, a control group is essential to determine whether a variable has an effect -- but here, the "variable" is the partner themselves, and the "control" is another person entirely, which is obviously not what was being proposed.
This is a classic SMBC joke structure: taking a common phrase or social situation and interpreting it through the lens of strict scientific methodology, producing results that are technically logical but socially catastrophic.