The physician at the door

An original fiction passage set in the nineteenth century.

“There is no cause for alarm,” Dr Mercer told Mrs Lane. “Your brother requires only rest.” He closed his case, pulled on his gloves and took his hat from the peg. As the servant opened the front door, a cough sounded from the room upstairs, slight but followed by a long silence. Dr Mercer looked towards the staircase. Then he returned his hat to the peg.

Identify the phrase which suggests that Dr Mercer no longer believes what he has told Mrs Lane.