We were proceeding northbound at 2900 feet, and the Gulf of Mexico was off our right wing, and Highway 77 was off our left wing. Jean and I were all bundled up because N7405B didn’t have a heater. I was concentrating ahead, when my peripheral vision caught something to the left and crossing below us. I looked to the right and below. I shouted to Jean, “Look at that!” and pointed down and to the right.