I feed right on the substrate and I heat my rats in water, so they are wet. Granted, I roll them into my rat towel (used only for that purpose) so by the time I bring them to the cage, they are mostly dry.

I've fed that way on aspen and now on the coarser kind of coco coir. Only once did I have to remove a piece of aspen from a snakes mouth. Most of the time everything falls off while they work the rat into the mouth. If a little sticks, they will digest it. They digest bones and in the wild all kinds of stuff gets transferred into their mouth during eating.

If a little is in their mouth, they usually work it out without a couple of hours.

It just hasn't been a problem for me.