How we change what others think, feel, believe and do
We are talking about X. Y is mentioned. The conversation changes to Y.
If you want to avoid talking about something, change the subject.
Pick something that will engage the other people. It can be completely off the current track or something related, but not really relevant. Something controversial or anything that arouses their emotions is often a good idea.
What about Christmas? Well, my aunt is coming next week.
This is expensive. Mind you, I heard that we might get a raise soon.
Yes, it is expensive, sir. Is that a scratch? No, it's reflection in the fine paintwork.
Red Herrings, if they snag the interest of the other party, can cause the conversation to change direction (and perhaps away from the direction the speaker does not want it to go).
When a word or sentence does not fit in with other words and sentences, the overall semantics are lost and listeners are confused. In that state of confusion they are open to other suggestions.