Two points of light chased by helicopters over Lake Greenwood, South CarolinaA group of approximately 10 people were on my back deck watching a football game and socializing when I started hearing a faint mechanical noise. At first I thought it was a train (there is a track approximately 1/4 mile from my house). After about thirty seconds it became clear that it was a helicopter. I thought at the time that it was quite strange for two reasons: first, I don't remember seeing any helicopters at the lake before, and two, it was dark.A friend and I ran down my steps and into the clearing near the water. We then saw that there were two helicopters flying very low and fairly fast. There was enough ambient light that we could clearly see the silhouettes of the helicopters. It was several seconds before I noticed that they appeared to be chasing two "points of light" that were traveling equally as low and fast, staying about 750 feet in front of the helicopters. They were moving independent of each other and the helicopters, but there was no "silhouette" of any kind associated with the two objects that I would estimate as being 3-5 feet in diameter.My friend works as a project engineer for a contractor. I am 37, working on my pilot's license, have some college, run my families' business, own a small business, am elected to a minor local office and have a 16 year old son that lives with me.