A Corpse
According to Reddit user tiorted726, garbage collectors can find all kinds of creepy things, even a dead body.
“I wasn’t a driver but a mechanic on garbage trucks for a large municipality. In my 4 years in that department we had to dump fully loaded trucks on the ground 2 times and spread out the load looking for a body; found one once. I decided not to look at it, I think I made the right choice.”