After watching this, I guess I now know that when Bruno talks while carrying Oscar's can, Oscar just hides his hand in the trash can to pull the wire. And it actually isn't that noticeable, except that Oscar stalls a bit in talking when telling Bruno to talk (and also quickly says "if I can find the controls"). I was recently watching the end of Follow That Bird, and hadn't noticed that his hand was down in the trashcan when Bruno spoke at the end (I've noticed Bruno already had his mouth open before he said his line, I guess Carrol Spinney already had Oscar pull the wire down before the line to make sure he was feeling it).