Which of the following is a common characteristic of horror films?

Unpredictable plot twists are a hallmark of horror films, as they contribute to the tension and suspense that define the genre. These twists often subvert audience expectations, creating moments of surprise and shock that heighten the emotional experience. Horror films frequently lead viewers down a path that appears clear, only to reveal a sudden turn that can completely change the narrative. This unpredictability keeps the audience engaged and on edge, enhancing the overall impact of fear and dread.

In contrast, the other characteristics listed are not typical of horror films. Happy endings generally counter the genre's focus on fear and dread, while comedic elements may appear in some horror-comedy hybrids but aren't a fundamental aspect of traditional horror. Similarly, high romance is often not a dominant element in horror films, which tend to prioritize tension and supernatural elements over romantic storylines. Thus, the presence of unpredictable plot twists is a defining feature that aligns closely with the conventions of horror cinema.