There's two kinds of blackberry here. You could call em small and large. Small ones are native, large ones are invaders from another continent. Anyhow, the "small" blackberry has very fine thorns that easily get lost in the skin, only to swell into tenderness and pain days later. Eventually, they harden into a benign cyst and move upwards, through the layers of the skin, until you can pinch them off with fingernails or clippers.