David Weaver
.not that you need to know it, but for anyone wondering...

If the bevel is being ridden and the sides of the mortise are clear, handle pushed toward waste side a little (which sounds pointless, but it helps the next), chisel lifted from the cut a tiny bit, then handle pushed back toward the uncut waste and pulled up.

The art of this is pushing the chisel toward the waste side enough to loosen things just a little, but not enough to break the shaving and have it topple down into the mortise.

If a chisel is inaccurately made, all of this stuff doesn't happen that easily. Even when it does work well, from a bunch of cutting of deep mortises today, the chisel gets pretty warm. Not hot, but interestingly warm.