Spin the egg on a flat surface; a hard-boiled egg spins smoothly and quickly
Stop the spinning egg briefly and release it; a hard-boiled egg starts spinning again right away
Shake the egg gently; a hard-boiled egg feels solid with no sloshing
Peel a small spot; a hard-boiled egg has firm, fully set white and yolk
Cut it open; a hard-boiled egg has no runny center
Place it in cold water after boiling; a hard-boiled egg feels firm all the way through
Check the shell after cooking; a hard-boiled egg usually has no soft or liquid movement inside