Why does it always happen when you're tripping?

[MDMA-4-ALL]

I was tripping hard one day and we needed to get aross town, so jumped in a cab. This was all at the height of the terrorist paranoia. Well we were driving along, me and my mate trying our hardest to keep it together (Keep in mind this is after 3 hits of liquid acid each). He reaches into his jacket and brings out a pen, and the cab driver freaks out, and starts demanding: What is that! Is that a bomb!
You can imagine what impact that had on two trippers trying to keep it together. Poor cab driver...
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MDMA-4-ALL (And acid too on that night)