She stepped over the threshold and walked into the room.
Tips
mistakes
This character is a heteronym - it has TWO completely different readings with different meanings: kǎn means 'threshold / hurdle' (almost always seen as 门槛); jiàn means 'cage / balustrade' (in 兽槛, 槛车 'prisoner cart'). Wrong reading = wrong meaning.
culture
Traditional Chinese houses had a high wooden 门槛 - sometimes knee-high - meant to keep out evil spirits, dirt, and wandering animals. Stepping ON it (rather than over it) was rude; this is the source of the modern figurative 'hurdle' meaning.
木 on the left is the tree radical, the pictograph of a tree with spreading branches. It marks 槛 as a wooden structure, grouping it with 栏 (railing), 框 (frame), and 桌 (table) - here a wooden threshold beam or cage.
监 supplies the reading, drifting from jiān to kǎn while keeping a related rhyme. Its sense of watching from above also fits: a 槛 either guards a doorway from being crossed or pens an animal under supervision.
