Blend shapes in 3D character design often feel stiff due to too few shape targets or unsmooth weight transitions.
Too few targets mean the model can’t capture subtle expressions—like a slight lip twitch or eyebrow furrow—leaving movements flat. Unrefined weighting causes abrupt shifts (e.g., jumping from neutral to full smile) instead of the gradual muscle build-up real faces have.
To fix stiffness, add intermediate targets (e.g., half-smile, gentle eye squint) or adjust weight curves in your 3D software. This mimics real anatomical movement, making blend shapes more lifelike.