At first glance maybe these words seem to be alike,but actually they are different from one another.
let’s explain them one by one and look at some examples to get the feeling of each one of them.
豆腐心(dòu fu xīn)
This is a very informal word.It means that based on one’s apparent looking or indulgence other people might think he also has tough heart or cruelcy. But actually and surprisingly he has a good heart and compassion and also ready to help people in need.In other words,someone’s looking,engagements etc. make us impressed that he surely is a bad person and cruel. But actually we are surprised to discover that he is a good person with a good heart. Some sort of a contract between the apparent and the actual truth.
(wǒ de yī gè péng yǒu ，zhǎng de wǔ dà sān cū ，zěn me kàn dōu xiàng shì gè hēi shè huì ，dàn qí shí tā yǒu yī kē dòu fǔ xīn ，zhī yào shì péng yǒu men yǒu xū yào bāng zhù de shí hòu ，tā dōu huì bāng zhù tā)
One of my friends really looks like a bully,like one of the undergrownd world.but actually he has a very soft heart.If some friends needs any help he is willing to give him his help.
(lián zài jiān yù lǐ de qiú fàn dāng zhōng yě kě néng yǒu yī xiē yǒu dòu fǔ xīn de rén )
Even in prisom may be a prisoner with a soft heart.
心软 (xīn ruǎn) To be softhearted / to be tenderhearted / to be kindhearted / softened (toward somebody else)
他心软了, 流下了眼泪。(tā xīn ruǎn Le , liú xià Le yǎn lèi )His heart was softened and melted into tears.
祖父是一位心软的老好人;他老是给我们好吃的、好玩的。(zǔ fù shì yī wèi xīn ruǎn de lǎo hǎo rén ;tā lǎo shì gěi wǒ men hǎo chī de 、hǎo wán de) 。 Grandpa is an old softie; he always gives us treats.
松口 （sōng kǒu）to give up and tell someone a secret or admit fault
(gōng sī de cái wù jīng lǐ yīn wéi tān wū shòu dào Le zhǐ kòng ，jīng guò liǎng gè yuè de zhèng zhā ，tā zhōng yú sōng kǒu chéng rèn Le zì jǐ de zuì xíng)
The company’s financial manager has been accused of corruption, after two months of struggle, he finally relented and admitted his crimes.
(jūn rén qiú fàn bèi shé mó yǐ hòu ，yī bān dōu sōng kǒu ，xiè lù chū mì mì )。
After being tortured, captive soldiers generally give up and release army secrets.