what as unusual about the phone calls with his mom

I can't find this section in my text. Do you have a date to match this question?

its about the calls that his mom makes

I am soooo sorry;

His mother's phone calls always took place on Thurday nights. Thursdays were also his mother's best days. She'd wait for him to come home from school, she'd bake, and sometimes she'd even hum or sing. In the evening, Adam knew his mother would disappear for an hour in her bedroom to use the phone. He never questioned her about it.