"Relax Slide" brush

Technical Support Modeling
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1

I’m following this tutorial on retopology and, multiple times thoughout the video, the guy uses the “Relax Slide” brush. The question is: by the way he uses it, it looks more like a smooth brush, but when I use it, it just grabs and “smears” the vertex, doing the exact opposite of smoothing the mesh. Am I missing any setting?

One of the parts where he uses the brush is 48:40.

2

You did not pay attention to the shortcuts displayed at the corner of screen.

When he uses the brush, he hold the Shift key.
That changes the brush behaviour, from its default sliding to a relaxing.