37. Tom, who owns a house, learned the previous day that his neighbor Jennifer was getting new sprinklers. That morning, Tom sees the plumber mistakenly installing the sprinklers in his own lawn. Tom says nothing, and then refuses to pay when the plumber hands him the bill, claiming that he never agreed to pay for the sprinklers. If the plumber can prove that Tom knew that the sprinklers were being installed mistakenly on his property and failed to prevent the installation, the court could make Tom pay for the sprinklers, based on: