Learn Spanish (Spain): ¡Qué susto! Ese perro es muy peligroso. - What a fright! That dog is very dangerous.

When using ¡qué! with a singular noun to make an exclamation, Spanish completely drops the article. You just put ¡qué! directly next to the noun. Saying ¡qué un susto! is a common trap for English speakers, but it is incorrect in Spanish.

Why use ese instead of eso for "that" dog?

Ese is the masculine singular adjective for "that", used when you specifically name the noun right after it, like perro. You only use eso when the noun is completely left out, like if you point at something unknown and ask "What is that?" (¿Qué es eso?).

Why does this sentence use es instead of está for "is very dangerous"?

We use es (from the verb ser) because being dangerous is described as a permanent characteristic or core trait of this dog. If you used está (from estar), it would imply the dog is only acting dangerous temporarily in this specific moment.

Can I use susto as an adjective to say I am scared?

No, susto is a noun meaning "a fright" or "a scare". In Spanish, you do not say you "are" susto. Instead, you use the adjective for scared, which is asustado, or you say you "have" fear (tengo miedo).