To get clothing fibers out of Velcro hooks, I've successfully used: a fine-tooth comb, a dental pick, a small pen knife blade (edgewise & pulling, not cutting), and my big fat fingers.

If it's snow, dirt, or mud, sometimes simply beating it against/over something--more like slapping it, I guess-- will work.

There comes a time, though, when the hooks are damaged beyond salvation, & it must be replaced, or perhaps augmented with a snap (did that a couple of times--especially on the waist tab of a pair of shorts--put the snap right in the middle of the velcro!).

Gluck haben!

David