What is "crumb brush"

Crumb \Crumb\ (kr[u^]m), n. [AS. cruma, akin to D. kruim, G. krume; cf. G. krauen to scratch, claw.] [Written also crum.]

1. A small fragment or piece; especially, a small piece of bread or other food, broken or cut off.

   Desiring to be fed with the crumbs which fell from the rich man's table.
   --Luke xvi. 21.

2. Fig.: A little; a bit; as, a crumb of comfort.

3. The soft part of bread.

   Dust unto dust, what must be, must; If you can't get crumb, you'd best eat crust.
   --Old Song.

   Crumb brush, a brush for sweeping crumbs from a table.

   To a crum, with great exactness; completely.