切忌 introduces strong warnings — common in instructions, safety notices, and health advice. It's followed by the action you must NOT do. Synonym: 千万不要 (qiānwàn bú yào).
mistakes
Don't read the 切 here as qiē (to cut). In 切忌 it's qiè, with the meaning 'urgent / earnest' — same character, different reading.
