The substrate is aspen chips. They usually fall off as the snake swallows, so I don't bother picking at them.
They don't splinter at all, actually. The wood is soft and smooth to the touch, quite nice to run your hands through imo. Not nearly as rough and pointy as cypress mulch. Plenty of hognose breeders use aspen chips without issue.
Not that it matters, but I usually use tongs and let my snakes strike midair. Sometimes they like to drag their food through the substrate though.