Probable the most ignored 'warning' ever. It says right on the box that you shouldn't brow into the cartridge. And you have another thing in there that only old-school gamer would get- turning the TV to channel 3!
Ah, yes, I remember that so vividly. Those were the days. If anything, that was the golden age of Nintendo.
It kind of makes you wish Nintendo made the NES a top-loading console to begin with, but then again, the system wouldn't be as memorable as it is now if they did that. (Yes, I am aware the top-loading version was made, but not 'til much, much later, but still.)