Crows use cars as nutcrackers.
I wasn't joking about my parakeet Fred. He would play (and masturbate) so hard with the swing in his cage that he'd routinely knock it down. (he'd also routinely fall off his perch out of excitement) Fred also had a ladder in his cage. When he first started doing all of this, he'd stare down at the fallen swing. One day I saw him at the bottom of the cage, swing in beak and he appeared to be struggling to get it up the stairs. I saw this several times. My roommate didn't believe me until he saw it himself. I got home one day and he was practically screaming "Fred tried to drag the swing up the stairs!"
I guess he managed to observe people putting the swing up and managed to make the association.
My fucking German Shepherd. We spend hours per week trying to stay ahead of this bitch. This is our fifth GSD and by far, incredibly far, the smartest. You always hope you are going to get a really smart dog, until you truly get one!
Don't forget the octopus. They're very good at problem-solving.
I liked the story of the oceanic lab which was finding its crabs eaten overnight with shells laying everywhere. They set up cameras and reviewed the footage the next day to find that one of the octopus would open its aquarium, crawl across to the crabs, have a meal and then crawl back to its home.