The call I keep replaying from last week

Monday mid-shift and I'm still thinking about a call from last week where the caller stayed calm the whole time — too calm, that flat voice people get when they've already decided how it ends. We talked them through it anyway. What I can't shake is how their voice warmed up at the end, just slightly, when they said thank you. Nobody clocks those moments but the people who are paid to listen for them.