Credit for this goes to RAVIOLICAPONI, and I'm posting it because I wish I'd seen his comment before I tried it.
This is glitchy. Make sure you do it like this:
After you get the key to the Baroness' room from Legrand, go up to the room and SAVE YOUR GAME.
Go inside to the far side. Starting with the portholes, look at everything in the room. You can press X to make sure that you aren't missing something. Click on everything until you can't click again. Work toward the front of the cabin. Make sure to get things like the paintings, mannequin, luggage trunks, alarm, and the cover in the ceiling.
This popped for me once I examined the lock on the door. I didn't have the tongs, and I didn't take a sample on the bed (although I did examine it). Like I said, press X to see if you've missed anything before you get back to the door lock.
If it doesn't pop, reload your save. Best of luck!