Why can i sometimes feel an intermittent pulsation/twitch under my left rib cage?

Pulsation: Possibilities include an irritability of that abdominal muscle, pulsation caused by the inferior surface of the heart's muscle or a prominent pulsation of the abdominal portion of the largest artery in the body-the aorta. The aorta may be palpably normally in a slender individual, but a normal sized heart usually isn't palpable in the abdomen. I suspect you're feeling benign abdominal muscle twitc

Normal: This is pretty common and just your muscle twitching which many have during times of stress, sleep deprivation or otherwise intermittently. It is not dangerous, and not sign of anything serious. Common places for this to be felt are the eyelid, the muscles of the ribcage area, stomach or legs.