The detectives have raided a house and found some suspicious white powder or liquid. One of them puts his or her finger in it, then either sniffs it or tastes it. They pronounce it's heroin or cocaine or whatever. Or if it's phony drugs, they announce "Powdered sugar!" Also done by drug-dealing baddies. Seen in almost every 1970s Cop Show. The mysterious white powder (almost) never, ever, ever turns out to be a deadly poison that kills our hero outright, despite the fact that he's found something, doesn't know what it is, and is stupid enough to put it in his mouth.