Undercutting gives life to a carving because it brings in shadows, drama.
I'm still working on the bottom edge of the shirt, the front shirt tails. The forms undulate and we are working into end grain, and this makes undercutting here a little tricky. To clean the surfaces and create neat junctions, you'll find slicing cuts, a 45deg. V tool and shortbent tools really helpful. Again, leave an edge of 1/8" 3mm. and don't undercut more than you need to to make the effect.