You know what you know.
Hello, in Riddick (2013), a group of bounty hunters planted a key operated mine on a locker with valuable items. But somehow Riddick (a most wanted convict) leaves a message on the locker that makes them suspect the locker and mine was tempered with. So now they are not sure if they should open it. One of the bounty hunters insists that it's dangerous.

BH#1: So, do you think sometime during the last few hours he got this (the key) off my neck without me noticing, did whatever he did, put the key back on my neck without me noticing? Is that what you're saying? Where did you get that theory from?
BH#2: There's a reason he is who he is.
BH#1: He's a convict. Not some Zulu warlock.
BH#2: You know what you know.
(BH#1 starts opening the locker.)

Could you tell me what "you know what you know" means here, please?

Thank you!

Question

You know what you know.
Hello, in Riddick (2013), a group of bounty hunters planted a key operated mine on a locker with valuable items. But somehow Riddick (a most wanted convict) leaves a message on the locker that makes them suspect the locker and mine was tempered with. So now they are not sure if they should open it. One of the bounty hunters insists that it's dangerous.

BH#1: So, do you think sometime during the last few hours he got this (the key) off my neck without me noticing, did whatever he did, put the key back on my neck without me noticing? Is that what you're saying? Where did you get that theory from?
BH#2: There's a reason he is who he is.
BH#1: He's a convict. Not some Zulu warlock.
BH#2: You know what you know.
(BH#1 starts opening the locker.)

Could you tell me what "you know what you know" means here, please?

Thank you!

Answer

It's a confusing phrase, and it's difficult to describe.

Basically, BH2 is saying that even though it sounds far-fetched and is difficult to believe, he is sure that Riddick  has the skill and knowledge to remove the key from BH1's neck, tamper with the mine, and put the key back without BH1 even noticing. Therefore, it's dangerous to open the locker.

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