2 sentences

1. 他见到老虎，心里就开始发怂。

   tā jiàn​dào lǎo​hǔ, xīn​li jiù kāi​shǐ fā​sǒng.

   When he saw the tiger, he started to lose his nerve.

   Source: Dong Chinese Dictionary

2. 他虽然嘴硬，但面对那个大块头时，心里明显发怂了。

   tā suī​rán zuǐ​yìng, dàn miàn​duì nà​gè dà​kuài​tóu shí, xīn​li míng​xiǎn fā​sǒng le.

   Despite his tough talk, he clearly lost his nerve when facing that big guy.

   Source: Dong Chinese Dictionary