This toothbrush looks clean, but is actually filled with concealed filth.
Examples (Wiktionary)
Mandarin
必须懂得,没有肃清的暗藏的反革命分子是不会死心的,他们必定要乘机捣乱。
必須懂得,沒有肅清的暗藏的反革命分子是不會死心的,他們必定要乘機搗亂。
bì xū dǒng de , méi yǒu sù qīng de àn cáng de fǎn gé mìng fèn zǐ shì bù huì sǐ xīn de , tā men bì dìng yào chéng jī dǎo luàn .
It must be understood that the hidden counter-revolutionaries still at large will not take things lying down, but will certainly seize even opportunity to make trouble.