On a TechCrunch‘s guest post, Nova Spivack, CEO of of Radar Networks, the company behind Twine, wrote:

On the iPhone you simply launch Siri and then proceed to interact using a familiar “chat” interface. You make requests or state goals to Siri, and then Siri comes back with answers, questions or suggested actions.

You can type to Siri in natural language and it does a pretty solid job of parsing your requests. But more impressive is that you can simply push the talk button on your phone and speak to Siri and it understands you. No need to type. It works surprisingly well. I also like the visual interface – Siri illustrates the progress of each dialogue with nicely illustrated cartoon speech balloons. It’s super easy to follow the conversation.