If they found suspicious items, such as fliers or simply the vague vibrations of freedom, the Stasi would seal the contraband with a dustcloth in foil. After a few hours, the cloth would be stored in a pickling jar, then the secret police would use the dust cloths to train their commie dogs to sniff out political dissidents. History hasn't proven that the dogs twirled their mustaches and wore monocles while sniffing out East Germany's dissidents, but history also hasn't proven they didn't.
Do you or don't you see a mustachioed fancy dog taking this group photo? Exactly.
Sometimes, the Stasi had to get sneakier to procure an odor sample, like breaking into people's houses and stealing their underpants. Yes, the Stasi went on actual panty raids. Samples were also procured after wiping down chairs following an interrogation, which tells you how those interrogations tended to go.
Adam Eastland/Stasi Museum
A shitty situation on multiple levels.