The best time I had with "powder" was in Customs at the old Perth Mail Exchange in the 1970's. An envelope had some sort of powder in it so it was held and a card sent to the recipient to come in and tell us what it was. In due course a middle aged lady came in with the card & I got the envelope and we start to discuss it over the counter.
She obviously quite honestly had no idea what it was and she actually poured it onto the steel-topped counter and we stared at it and both wondered aloud what it is. (This is well before the days of anthrax scares or quick drug testing kits.) After a while she finds a small note inside to the effect that as she knows her "Uncle Joe" had recently died and as she was his favourite niece the family thought she would want some of his ashes.
I am not sure who was the more horrified of the pair of us but I quickly brushed up what was left of Uncle Joe and put him into her somewhat unwilling care. She left with much protestations about why on earth anyone would do such a thing and I went and had a good wash-up.