How can I prevent Siri from responding unexpectedly on my Apple Watch?

I think my Siri has gone mad!

She talks to herself. When I'm jogging, each mile she (or they(or it?)?) announces the time etc for the current split. If I (quite naturally) raise my wrist at this she/they/it answers her/their/its self with for example

"It doesn't look like you have an app named 'Split'.

You can search for it in the App Store." With a convenient "Search the App Store" button.

It's really quite amusing, but I'm going to have to learn not to raise my wrist...

[Re-Titled by Moderator]