If you look just behind the inlets you will see a Negitave pressure door open. This was to let in additional air at low airspeeds so that the jet engine did not collapse the fusalage. At higher airspeeds the inlets will pressurize the fuselage plenum and the door closes.

Are you sure this is not the BD-5? That sure looks like a prop turning on the tail and a blur behind the aircraft, in line with where the prop would be loks like a prop turning.

The BD 5 played a roll in a James Bond movie. It rolled out the back of a moving tractor trailer and flew away.
At flight idle the plane was hard to slow down so Jim Bede installed clam shells on the engine.
Flying magazine did an article on it some where around 1981.