i think that Sherrill illustrates this as a 'saw catcher'.
As JP says, i walk the kerf under cut to point of faiure, maybe even sliding the saw back and forth to detect the least amount of drag as i cut up. But then as Murph and Kevin refer to, i take out the sides to remove some more support, walking the cut closer to failure; without fear of the saw getting pinched. Also this leaves less fibre to cut through for a faster cut, on the final release, for wider control of cutting speed (you can always slow it down),a nd precise, all at once release. i think that going in front of the undercut creates the saw catcher effect with so much leveraged pull pulling back and down. Coming behind undercut, tends to make green end not fall as early, if you can get that kerf undercut 'slam' closed, and release suddenly; i beleive that you can get the jump effect. If it closes slower, or doesn't release all at once, i don't think it can get that 'pop' that jumps. In topping this effect turned 90* can make a top jump a fence etc.
In felling this would be a kerf dutchman, and pretty dangerous with all the leveraged mass thrown into such a devised machine, giving a normal face cut, and continuing the horizontal cut past the down stroke, can make another similar machine, but not so violent and powerful. But it still is a kerf cut for that is the main inside hinge, and the faces will close early, doing this to one side (leaning)can push off to the other side from that buildup, and leave more hinge pulling to that side that is being pushed to all at the same time. Some of this stuff can give desired effect to crane jobs, by setting the crane up to take or snap off the piece just right.
In bucking these same things can be used, jsut watching all tensions and forces, you can make an instant release sometimes, or 2 kerfs missing each other for a 'Z' fracture/limb lock.
Jumping back toward you/trunk is usually the biggest problem, getting a straight drop down is easier, or slight turn to the side and straight down can be easier, more positive and sufficient. Using any down cutting technique that releases immediately all at once, i think can bring about a straight cut as the energy flows immediately down instead of back and down. Once again the 'box' precutting a 'U' underneath, for faster saw speed and more immediate trigger to release helps. The final cut can come straight down into the undercut. Some things are small enough, that they don't need to be undercut, the speed of the saw alone provides a sudden enough release. A faster saw (020/200 or 335 etc.) can get the next level of diffuculty just as well. My next strategy is to cut across slightly on release cut or give slight turn to load, so that at release a portion of the energy is thrown sideways (even if not visibly); scheming that that part of the total force is now not moving down, there fore less likely to pull back, yielding straighter drop down. That strategy can work with an under cut too.
Sometimes i do a 'Vertical Speedline' (nice term) by not lowering a load all the way slack, and letting that be a lower anchor with everyone clear.
