Well, one of the older actors is heading to the back of the building, and gives a signal of “waiting for cue”. It takes you a moment to catch on – she’s gotten ahead of you in the plan. She’ll make noise on your signal, which will make your warning seem more plausible.
Now you just have to figure out what you’re going to actually say. It doesn’t make much sense to you to be direct in asking the questions you want to know the answer to – if this person were in trouble and could tell you what was going on, they’d just do that. Asking direct questions would just tip your hand to anyone hostile listening in.
Well, your best bet is to play off what they’ve said, not any hunches.
“How can you be so sure? This place is pretty decrepit. Might be any number of holes big enough for someone to slip through.”
“Safe! I am safe here!” the voice cries out, in a tone that very much does not sound like someone who actually thinks they’re safe. “No one can hurt me! Leave, leave!”
Naturally, this is when you give the signal, and the actor at the back starts knocking on the building.
But the response is something you never expected.
The knocking silences them completely mid-sentence, almost as if someone pulled a plug out of them, they only continue answering in unison with the knocking
A different voice continues to answer, but as if it were the same person
The voice gets angry. A bright light starts shining from within the entire building, it doesn’t even look like it’s nighttime anymore
The voice calls out to Bert specifically
A strange substance starts seeping out of the building, the voice screeches horribly