I grabbed my guitar and watched my right hand as I played muting strings, both using a pick and finger picking. While it is not the same thing, I liken it to hitting harmonics at the 5, 7, 12 and 19th frets. To mute I rest my hand on the bridge and let just a little hang over the bridge to lightly touch the string(s), almost like using harmonics, but to mute them. It does not seem to matter if I have a pick or not or what string, I still get the mute using the heal of hand just below the bridge. Use the pentatonic to learn muting on each string or whatever scale you like.