4 sentences

1. 看到她，我的心跳不由自主地加快了。

   kàn​dào tā, wǒ de xīn​tiào bù​yóu​zì​zhǔ de jiā​kuài le.

   Seeing her, my heart began to race involuntarily.

   Source: Dong Chinese Dictionary

2. 由于寒冷，他的身体不由自主地抽搐了一下。

   yóu​yú hán​lěng, tā de shēn​tǐ bù​yóu​zì​zhǔ de chōu​chù le yī​xià.

   Due to the cold, his body twitched involuntarily.

   Source: Dong Chinese Dictionary

3. 听到那个恐怖的叫声，他不由自主地打了个冷颤。

   tīng​dào nà​ge kǒng​bù de jiào​shēng, tā bù​yóu​zì​zhǔ de dǎ le gè lěng​chàn.

   At the sound of that terrifying scream, he couldn't help but shudder.

   Source: Dong Chinese Dictionary

4. 由于光线突然变暗，他的瞳孔不由自主地放大了。

   yóu​yú guāng​xiàn tū​rán biàn àn, tā de tóng kǒng bù​yóu​zì​zhǔ dì fàng​dà le.

   His pupils dilated involuntarily as the light suddenly dimmed.

   Source: Dong Chinese Dictionary