I produced this strangely satisfying sound by dropping a watermelon-shaped canning tomato into a dishpan full of water. Have to get that just about right to get this result. For my purposes i needed to repeat it, but you can do that. It's unlikely that two objects tossed into liquid will sound exactly the same, but it's possible to modify one of the two "ploops" by changing amplification, pitch and even to shorten the waveform to make them sound different. If you need that done let me know.
Author: Nuncaconoci