Imported object moving alone: hidden script?,Why is the imported object moving without any script?

Hi, I'm new to Unity. I have just imported an object, changed its materials, gave it gravity, but when I hitted "play" the object started to dance and flying away. I checked its settings but I couldn't see any script attached. The rest of the objects behave as expected with gravity. I could change the object but I don't like the other available options. Can anyone give me a hint? Thank you!,