Never ask a woman

The wife told her husband the oil light is on in the car. He told her to get some oil and add it to the engine. Look for the cap that said OIL then take it off and add it in. A couple hours later she came back in the house all flustered. I can't seem to find it, there's the windshield wiper cap, an 710 cap, a brake oil cap, but no OIL cap.