The following are several ways to describe "frightening eyes":

1. His eyes are cold and sinister, as if he can see through your heart.

2. Her eyes flashed with a dangerous light that made people afraid to look at them.

3. His eyes are full of threats and malice, making people fearful.

4. Her eyes are sharp and fierce, as if they can pierce your soul.

5. His eyes are gloomy and terrifying, making people shudder.

6. Her eyes are full of hostility and vigilance, which makes people feel uneasy.

7. His eyes were like two cold stones, which made people feel heart palpitating.

8. Her eyes are like an abyss, intimidating.

9. There was an inexplicable fear in his eyes, which made people fearful.

10. Her eyes are like cold blades, which make people feel stinging.