How do snails reproduce?

[rs1831]

I have a few snails that are positioned near the top of my tank and they are releasing stuff into the water. They've been doing this for a few nights now.

Thanks.

 

[GhostCon1]

Is it a pellet shaped object? My snails do that everyone once in a while... it's waste

Although, I thought snails laid egg clusters... maybe some release gametes into the water.