This is by far not the first time I caught my cat plucking the ukulele, only this time I had the camera ready and was able to provoke him to do it again. One might argue, he incidentally touched the string, but then I have observed him several times going over to my ukulele, plucking a single string very deliberately with one claw and his facial expression made very clear, that the resulting noise was anything but unexpected.

He also plucks an acoustic bass from time to time, but he prefers to misuse it as a drum. (less info)