How to nudge my players in the right direction?
So, I added (and i know some people here HATE this, but don't flame me for that) a false hydra to the campaign. I felt it worked with the unsettling metal stress and trauma that CoS is famous for. It's not quite Gothic horror, but just enough adjacent it can be complimentary.
I didnt want to ruin any current normal plot line in any of the towns, so I made a new town. Dämmerfeste. It's located on the Svalich road between the Tser pool encampment and Vallaki. The lore of it is the now mad mage had built this town as a basepoint of his revolution, so they built it so Svalich road passes right through the town as it's center road. It had high pallisades, like Vallaki, but no gates.
Once the Mage "died" they town continues as just a town with a ghost of its original purpose remaining. Strahd doesn't concern himself with this petty resistance, thinking the land will put them in their place.
The dark powers caused the hydra to form from the mists, and it's hiding in a sinkhole cave in the woods outside the village. Strahd enjoys the psychological torment it inflicts on the villagers, so he ignores it. (Remember it's only been a year or so since his fight with the Archmage, so the village isn't much older than that.
Now to the problem.
Two of my players never heard of a FH. I dropped as many hints as I could (wrote a short book they found un the blood in the vine that had legends of things that may or may not exists in Barovia. One entry was the many-headed singer, and told the reader to plug their ears) and one player knows what it is, but is hiding it well, because player knowledge vs character knowledge and all that. They also have ireena, ismark, and donavich with them (the players convinced him to come to vallaki with them for safety after he lost everything, and then the tarokka named him as their fated ally [actually unplanned])
So, basically I wrote the statblock, basing it off stuff I found, and similar things (like the Silence from Dr. Who) amd made anyone who hears the song need to make an 18dc wis save or forget the hydra and what it's clearly done. If they know of the hydras existence, this is a DC 12 instead, made at advantage. However once you stop hearing it, such as if you plug your ears, or mpve outside the range, all the memories come flooding back (which also have a DC 15 Wisdom save, resulting in a lose of reaction for that turn (always) and a disadvantage on all d20 rolls made that turn (on fail)
How to i nudge the players to the sound based clues. Everytime they've checked things, I kept telling the higher rollers they felt something off all over the village, like a thrum or vibration, which was stronger when they were in the cellar of a house (because it's underground)
The players who has heard of a FH tried using the knife in the ground trick to try to better check the vibration, but as the character got a concentrated dose of the song, I asked them to remake their save, and they nat 1'd it. While I don't do crit fails for skill checks, it's still a failure of more then 19 or 15, so he suddenly forgot, and now my players lost they best lead.
Tldr; I put a false hydra in CoS, players are loving the environment, but I don't know how to nudge them to discovering it. Only 1 player is left who hasn't fallen for the hydra song, and she doesn't know what a false hydra is, despite my layering or sound based clues.