First, how do you know what the cop "should know about"? What he should or shouldn't know about is subjective. You might ask yourself, "what do I want this cop to know about?" It is unlikely that the answer to the question of what you want the cop to know about is "weed", pills, stolen property or the many other answers some drivers give in response to that question.
Second, it is sometimes a fishing trip by the police just to see if you answer "yes", or what else you might blurt out. That gives them what they need to interrogate you further. These questions are posed to drivers in an awkward syntax to make the nervous driver feel even more awkward. You don't have to fall for it. "Why do I smell ____ (whatever he claims to smell)?" How should you know why he smells whatever it is he claims to smell?
Everything you say in these threshold uncomfortable encounters with the cops can come back to bite you in Court if you get charged with possession of marijuana or under New Hampshire's DWI laws. Protect yourself, your license and your freedom to the extent you can. You have the right to "Lawyer Up and Shut Up" when the cops start to question you!
You can choose to talk with the cops but you cant be forced to do so. Please watch this brief video:
CALL TO ACTION:
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