Montresor ensured no servants would be around by saying that he would not be home until late that night, so don't leave the house, knowing they would leave the house. So since they left the house he would be able to bring Fortunato to his catacombs to do the crime.

Well in theory the gravitation substance can be found in many places in the world but as we all no it is very hard to accumulate. many people have died looking for this but only some succeed but the rewards are crazy im talking unlimited money flight laser beams and much more