偷偷 + Verb
偷偷 (tōutōu) means "secretly" or "stealthily." It is a reduplicated adverb derived from 偷 (to steal), used to describe actions done without others' knowledge. Place it before a verb, as in 偷偷进入 (to sneak in) or 偷偷看 (to peek).
他偷偷给女朋友准备了一份生日礼物。
Tā tōutōu gěi nǚpéngyou zhǔnbèi le yí fèn shēngrì lǐwù.
He secretly prepared a birthday gift for his girlfriend.
小猫偷偷跳上了桌子,吃了一块鱼。
Xiǎo māo tōutōu tiào shàng le zhuōzi, chī le yí kuài yú.
The kitten secretly jumped onto the table and ate a piece of fish.
弟弟偷偷看了我的日记,真让人生气。
Dìdi tōutōu kàn le wǒ de rìjì, zhēn ràng rén shēngqì.
My little brother secretly read my diary, which is really annoying.