Pick up the eggplant and feel its weight. A ripe and healthy eggplant should feel heavy for its size. If you are not sure, try picking up a few other eggplants to get a sense of what they weigh.
Turn the eggplant around, examining it carefully for dents, bruises, indentations or discoloring. A perfect eggplant should have none of these deformities. A damaged eggplant might be bruised, tough or rotten inside. Some eggplant varieties are naturally striped or mottled; this is perfectly acceptable and should not be considered discoloration.
Hold the eggplant in the brightest light you can find and look at its skin. It should be smooth and glossy rather than dull, puckered or wrinkled.
Poke the eggplant gently with one finger. A ripe eggplant will give slightly but immediately spring back to shape as soon as you remove your finger. An overripe eggplant will dent permanently, while an under-ripe eggplant will not give under your finger except with very forceful pressure.
Squeeze the entire eggplant gently, moving your hands all over its surface. If you feel any especially soft spots, the eggplant is probably internally bruised.