Switch out the dust

You’ve got a bad feeling about this dust. You quickly spread it out in a corner of the room then start gathering dust from the shelves. Using your hand you sweep the dust into the open sack then quickly tighten it back up. You can hear her coming and barely manage to put the sack back on the shelf before she re-enters the room. You flash her a sweet smile hoping she won’t suspect anything. She smiles back and walks over to the shelf

“Now. Where was I? Oh yes I was going to show you something important. Stay right there.” She retrieves the sack once again and stands in front of you emptying its contents onto her outstretched palm. You pretend to look surprised as she shows you the mound of dust.

“So it’s dust? I don’t unders.....”

Suddenly she leans in and blows the dust straight in your face. You cough and stagger back but otherwise feel fine. She laughs and looks at you expectantly. Clearly she expects you to pass out.