Last picture, under the exhaust pipe in the lower right - What's that part lying on the floor??
The last time I had my car out I only had the driver's seat installed and stopped back at the house to get a heavy blanket to toss into the passenger seat spot as a sound deadener. As I was crossing the garage floor with the blanket (the car was still outside) I spied a 1/4" X 20 nut lying on the floor.
Major panic ensued.......
Then, when I got back from the second ride (a little shorter than the first stage) I realized that it was one of the nuts holding the seat attach hardware under the car and I had missed picking it up when I pulled the seat.