The ability to compose a text or Hangouts message using only your voice on Android Wear is really convenient. But dictating a message via voice isn't always possible. For those times when you're too embarrassed to talk to your watch, or the surrounding area is too loud for the watch to understand, Google included the option to send a reply with just a few taps.
When viewing a message you can swipe to the left to bring up the Reply button. Tapping on the button will immediately enable the microphone. What you may notice at the bottom of the screen is a small blue circle with some text next to it. This is where you will find a shortcut to a list of quick replies. By swiping up on the screen you can view a list of predefined messages.
Scroll through the list and tap on one of the messages to send it without any further interaction. The messages are short in nature, ranging from "Yes," "No," and "Thanks" to "OK, let me get back to you." Currently there's no way to customize this list, but hopefully that will change in the future as updates roll out.