What is this? Golfball sized egg sack like thing that was slimey and when we poked it, it oozed yellow slime??

It was growing under a large peice of plywood...I'm afraid I killed an alien lol. It was very gross looking, and was in a sticky web type thing that attatched it to the wood. When we smashed it wwith a rock (lol) it oozed a gooey secretion that was the color of an egg yolk. I think it may be a slug egg nest or something but I'd like to know what it was for sure. Googling didn't seem to help me too much...And it was quite disturbing to watch. I hope someone can tell me what it was. :]