arangosh> a1 = db.example.insert({ a : 1 });
{ 
  "_id" : "example/478946357", 
  "_rev" : "478946357", 
  "_key" : "478946357" 
}
arangosh> db._remove(a1);
true
arangosh> db._remove(a1);
[ArangoError 1202: document /_api/document/example/478946357 not found]
arangosh> db._remove(a1, true);
false