Is there any phrase or expression that can be used to indicate that someone who does not actually know something (about someone else) is trying to pretend as if they knew it (or talking in such a way that implies they already know it) to maliciously extract information from another person or get that person to admit it?

For example,

> 
> John: Hey, Jimmy, How's the new project?
> Jimmy: What project?
> 
> 
> 

John is pretending to know something that may or may not be true to gather information.

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**Edit:** The word is not exactly "bluffing". Bluffing is more like lying or bragging.  

I heard an exact match in a movie. I cannot remember what the verb was:

> 
> I was trying to \_\_\_\_\_\_\_ on you.
> 
> 
>