The spare chair

An original fiction passage set in the nineteenth century.

Mrs Ellery had laid five places, although the letter promised only four visitors. At the fifth she placed the chipped blue cup, turning its damaged side towards the wall. When her daughter asked whom they expected, she said that a house ought always to have room for a surprise. Yet whenever a wheel sounded on the gravel she went to the window, and each time she returned without speaking. The fifth chair remained pulled a little away from the table, like a question nobody wished to answer.

Identify the phrase which suggests that the family is avoiding a difficult subject.