Don Stephan
Especially with softer woods like pine and poplar, when chopping in from each side at the base of the recess that receives a tail or pin, the center of the opening will break back towards the other end, a phenomenon I have seen referred to as spelching. This is not a clear description I know, but I do not have a picture to post.

This seems to occur regardless of how hard or softly a sharp chisel is tapped. With pine the breakout can be within 1/16" of the surface of the board. The 2nd practice board this morning is swirling grain in cherry, and the spelching is much less, perhaps because the grain direction is not parallel to the edge of the board. I understand the end grain that breaks out does contribute to the strength of a glued dovetail joint, but spelching in softer woods can be frustrating. Has anyone found ways to reduce it?