brains
Explanation
The comic presents a "horror movie idea" in which "all the headless hunks from romance novel covers are alive and out for revenge." We see a muscular, shirtless, headless male torso (the classic romance novel cover figure) menacing a woman. The torso moans "BRAAAINS!" and the woman responds, "You could have emphasized our BRAAINS!" -- implying that the headless hunks want brains because they literally do not have heads.
The humor operates as a mashup of two genres. The headless beefcake is a well-known visual trope from romance novel covers, where male models are often photographed from the neck down to emphasize their physique while keeping them anonymous and interchangeable. The comic literalizes this artistic convention -- if these men truly have no heads, then of course they would want brains, just like zombies in horror movies.
The woman's retort adds a layer of feminist commentary. When she says "You could have emphasized our BRAAINS!", she is pointing out that romance novels (and their covers) tend to emphasize physical attributes over intellectual ones. Her complaint is that the genre could have valued intelligence ("brains") more, but instead it objectified bodies -- and now, in poetic justice, the objectified bodies have come back demanding the very thing that was left out. The joke works both as a zombie movie parody and as a wry critique of how romance fiction represents both men and women.