I should probably be embarrassed at how many I bought, however yesterday the samples did a good deed - a rat was taking up lodging in the wall here (I saw it outside, definitely a rat) and it took 3 tries to get my landlord and landlady to even listen to me about it. It was chewing in a wall near electrical lines, but they wanted to wait for this coming week to call an exterminator to deal with it. Uh, no - get some rat traps NOW! Then they took hours to do that. I was stressed at listening to it chew in there and waiting for them to act, during which time I sat and cut up white stickers, put them on the tops of all the vials, and marked each with a bit of the ink inside the vial to identify them in the rack. That minor task, being enjoyable, was effective at preventing my stress level from over-flowing.
(Before anyone asks, I had no way to get to town to buy traps myself, hence having to wait on them. And yes, I beat on the wall close to where the rat was, trying to scare it off. Instead it sat there and squealed/screeched, whatever you call that noise they make.)