他拔出一把刀，刺伤了她。

He drew/pulled a knife and stabbed her.

在犯罪现场发现了一把刀。

A knife was found at the scene of the crime.

在有人受伤之前把刀拿开。

Put that knife away before someone gets hurt.

小心，否则你会被那把刀割伤的。

Careful or you'll cut yourself with that knife.

左手拿叉子，右手拿刀。

Hold your fork in your left hand and your knife in your right hand.