The waveform of Siri interface on Apple Watch Series 4 differently works with the behaviour of how Siri is on other devices. Thereby the animation hence states with the waveform in sync with change in volume with how Siri on iPhone works.
The way Siri animation works looked upon Apple Watch Series 3 or earlier with the rainbow colour freely dances, continuous as the Siri modal view is presented.
With the animation not synchronized completely and completely canned with the user input basically is by playing video. Hence with a pretty poor user experience, one implicit connection of the product without any real-time feedback.
With Siri on iPhone, iPad, Apple TV, and macOS do reflect with actual speech input who bounces where a lot is done speaking and the user takes a breath. Hence with a known fact, Apple Watch Series 4 can run watchOS 5 brings the wrist to the same behaviour. For example, a video put together, with a comparison of my Series 3 and Series 4 side-by-side, Series 4 is more alive punctuated by a flash colour on the screen.
One thing considered quickly by putting together with the fact on how better the Series 4 behaviour is where older watches has no technical reason left stale long already.
By putting a cork with this feature, looks like a series of grey lines, changes in height, without finding a newfound dynamic animation ability. Hence opening of a sheet on the Watch, compose a text message through your voice which does not say anything. A pretty stupid thing about Apple which did not deploy is the improvement on Siri waveform which can follow a future software update.