In addition to text comments, you can reply with videos.

Its pretty easy. For any video in the Received or Featured area, touch the thumbnail for the video of interest.

Touching the thumbnail, you will go to the video detail page.

Touch the "Reply" icon at the bottom of the details page.

You will be presented with three options:

(1) MyMedia - select any video in Thwapr to use as your video response and then add your text comment

(2) New - capture a new video to use as your video response and then add your text comment

(3) From Device - import a video from your Camera Roll to use as your video response and then add your text comment

The owner and any other commenters will be notified of your video response.