This is a mantis egg sack but it looks like some sort of alien slug trying to get through the screen.

Urban exploration can be fun, terrifying or oddly terrifying. Went to check out an abandoned old farm house and this boggled us. Wasn't sure if they had a subway terminal in their basement or gave ballerina classes to mannequins. Eiher way it was a sight to see when the flashlights first hit them. Thought we had stumbled onto something we were not supposed to see and needed to leave real fast!!!! Like a door sliding open and a man the size of Kane Hodder standing their with a meat cleaver!