Ran over something, what to check underneath?

Ran over something on the highway today. Not sure what it was, but it looked like plastic, was about 2 ft. long and had a triangular cross section. It was immobile on the pavement when it appeared out from beneath the car in front of us. So it wasn't high enough for most cars to hit. Unfortunately the Prius is low, and while I couldn't avoid it due to cars on both sides, I was able to position it to pass right down the center of the car. As it went under it made two fast "chunk chunk" noises. Pulled over in a parking lot a few minutes later to inspect and did not see any damage. The front plastic was all intact (the lower spoiler was removed long ago, had it not been, I'm sure this would have taken it off.) The gas tank wasn't leaking and I didn't see any dings in it, but the angle and light weren't great. Looking from the front of the car the two lowest points were the cat shield and a pipe somewhere between the shielded cat and whatever comes next (muffler?). Drove the car for another half hour or so and nothing else untoward happened (no CEL, no puddles, no odd noises.)

Tomorrow when the underside of the car is cold I'm going to jack it up for a better look. Going to give the gas tank a better look and shake the exhaust system a bit to verify none of the connectors broke. Anything else that I should look for?

Thanks.