one friend had his car ashtray examined. they took it away for a while, then came back with a test-tube full of liquid and said it tested positive for traces of pot. (he never touches the stuff) they bawled him out, but ended up letting him across anyway (?)

another guy had put his prescription pills in an unmarked bottle. They seized his car, and it took weeks to get it back!

strange border events seem pretty random, and rare. most people just get waved through, "have a nice day", but you never can tell. Maybe the guards just get bored.