When someone changes the subject fast, the old subject might be the important one.

A sudden swerve is information. People do not redirect away from things they feel nothing about, so the speed itself marks the spot, whether because it hurts, embarrasses them or involves something they are not ready to say. The new topic is often a perfectly good one, which is what makes the move easy to miss.

Notice the handbrake turns this week rather than following them automatically. You do not need to drag anybody back, and you can come back to it later, once, gently. If somebody does it to you, it is worth asking yourself what you were steering away from.