brown oval sticky slug type thing?

I found this thing, i don't know what it is. Its outside stuck on my cement outside my back door. It is brown, oval, and i think its some sort of slug but i have surfed the internet with no luck. it is about 2-3inches long and 1-2inches thick. And it is SUPER sticky i tried to move it off with a stick but it is that sticky, it is just sticky on the bottom, and squishy on the top. It kinda has this thin black line going down the center of its back. i didnt really wanna hurt it so i just left it there. It wasn't there last night, but its here now in the morning. i guess eventually it should move. but does anyone know what it could be?