GRAMMAR DETAIL

かと思うと

just when it seemed that

Expresses that an unexpected new state appeared quickly, immediately after the preceding state was noticed.

Examples

空が急に暗くなったかと思うと、大粒の雨が降り出した。

Just when the sky suddenly grew dark, large raindrops began to fall.

彼は笑ったかと思うと、急に黙り込んだ。

He laughed, then suddenly fell silent.

雨がやんだかと思うと、今度は強い風が吹き始めた。

Just when it seemed the rain had stopped, a strong wind began to blow.

Structure: かと思うと after a ta-form verb presents a rapid development immediately after the first situation is noticed.
Basic usage: 彼は笑ったかと思うと、急に黙り込んだ。 describes an abrupt shift from laughter to silence.

A rapid shift after noticing
- Despite か, this is a linking expression framed through an observer's perception, not a question addressed to someone. The silence following 笑ったかと思うと is presented as a swift, unexpected change.
Comparison with a planned sequence
- 食べてから出かけよう proposes a planned order of actions. かと思うと is better suited to describing a rapid development observed unfolding than to proposing such a plan.