Learn Spanish (Spain): Él dejó de sentir aquel escalofrío y el temblor desapareció. - He stopped feeling that shiver and the trembling disappeared.

The phrase dejar de followed by an infinitive is a specific structure that means 'to stop doing something'. Without the preposition de, the verb dejar simply means 'to leave' or 'to let'.

Why does the sentence use aquel instead of ese for 'that shiver'?

While both mean 'that', aquel indicates a greater distance in space or time. In storytelling or narrative past contexts like this one, aquel is often used instead of ese to emphasize that the event or feeling is firmly in the distant past.

Both dejó and desapareció are in the preterite tense. Could the imperfect be used here instead?

Not without changing the meaning. The preterite is used here because stopping and disappearing are framed as completed, sudden events that move the story forward. If you used the imperfect (dejaba, desaparecía), it would sound like he was in the process of stopping, or the trembling was gradually fading away in the background.

What is the difference between an escalofrío and a temblor?

An escalofrío is specifically a 'shiver' or 'chill', usually caused by cold, fear, or a sudden emotion. A temblor is a broader term for 'trembling' or 'shaking', which can apply to the body, a voice, or even the ground.