What does 谈晋倏忽之间勾了下嘴角 mean? I found a novel on my Kindle (喜欢你，我也是) which seem like a teenage romance, and seems fairly readable and interesting.  I'm at the start, and thus far Zhang Kankan 张侃侃 and seems to have been tricked into a blind date with Tan Jin (thinking she's there to 补习); they're both teachers.  Currently, Tan Jin seems to be confusing her.

It has the line:


  “哦？”谈晋倏忽之间勾了下嘴角，“金主让你做什么就做什么，是这个意思吗？”
  喜欢你，我也是


I don't understand the part in bold.  (It seems Tan Jin is also confusing me.)


  "Oh?" Tan Jin suddenly (?) [倏忽之间] hooked the corners of his mouth (?) [勾了下嘴角], "Bankroller makes you do something, you do it, is this the meaning?"


Question: What does 谈晋倏忽之间勾了下嘴角 mean?
哦？”谈晋倏忽之间勾了下嘴角，“金主让你做什么就做什么，是这个意思吗？”


倏忽之间: suddenly

For 勾了下嘴角 you could perhaps write: 轻蔑 or 冷笑 

谈晋倏忽之间勾了下嘴角，
Tan Jin suddenly snarled,

“金主让你做什么就做什么，是这个意思吗？
"If the boss wants you to do then do it, is that what you mean?"

You could replace 倏忽之间勾了下嘴角 with either: 冷笑道 or 轻蔑地说道

谈晋冷笑道， : Tan Jin, with a sarcastic smile, said,
谈晋轻蔑地说道，Tan Jin disdainfully spoke,