2 sentences

1. 他一不小心，把水杯打碎了。

   tā yī​bù​xiǎo​xīn, bǎ shuǐ​bēi dǎ​suì le.

   He accidentally broke the glass.

   Source: Dong Chinese Dictionary

2. 她把缝补衣服用的针插在布垫上，防止一不小心掉在地上。

   tā bǎ féng​bǔ yī​fu yòng de zhēn chā zài bù​diàn shàng, fáng​zhǐ yī​bù​xiǎo​xīn diào zài dì​shang.

   She stuck the sewing needle into a pincushion to prevent it from accidentally falling onto the floor.

   Source: Dong Chinese Dictionary