Trying not to giggle, you follow quietly these guys around all the mansion while they were busy making photos to old stuff and grabbing some old jewelry that maybe has some vallue. You, stayed behind a door thinking how you could mess with your future big sisters. When they turn their back on you, you decided that this was the moment to act.
Grabbing a pebble from the ground, you hold it in your left hand for a moment and throw it at the boy on the left with enough force to make some pain when it hits him. It has desired effect and the both of them jump on the site at the same time when your target screams of fear an pain.
The object of your joke turns to his partner with a sour face preparing some accusations when they become aware of your presence.
"Eh, isn't that the mannequin that was at the entrance?"
"Holy shit. I think you're right."
Of course you remain completely immobile, like when you are shut down. For them you are just another inanimate object.
They both look like they just shit their pants and you have to use all your willpower to avoid laughing as they get closer to you.