GRAMMAR DETAIL

～出す

to suddenly start doing

Indicates that an unexpected action or event suddenly begins.

Examples

赤ちゃんが急に笑い出した。

The baby suddenly started laughing.

電車が駅を出ると、隣の子どもが急に泣き出しました。

When the train left the station, the child next to me suddenly began to cry.

Structure: Add 出す（だす） to a verb's ます stem to express the sudden onset of an action or event.
Basic usage: 赤ちゃんが急に笑い出した。 describes the baby suddenly starting to laugh.

How the onset is presented
- 泣き始めた states that crying began, while 泣き出した highlights the moment of bursting into tears. 出す readily conveys an abrupt transition.
Inflecting the final part
- In 笑う→笑い出す→笑い出した, the first verb stays as a stem and 出す is inflected. 泣き出しそうだ describes seeming about to start crying.