It is not under any circumstances, a good idea to hit an object with a hammer if you do not know what the object specifically is, or what might be contained inside it.

Of course, sometimes it's not a good idea to hit an object that you can identify with a hammer either.

As I come up with examples I beg to include the idea that it's certainly not a good idea to hit any living thing with a hammer, and it is also a really bad idea to hit something that once was living, no matter how recently that might have been. The winning argument there would be "guts".

But who would have known really that the best rule of all to impose on a group of children in the wild regarding hammers is do not EVER (ever ever EVER) hit an inkjet cartridge with a hammer.

Especially if you put it on top of a rock first.

Just a bad idea resulting in large spatters of blue on your person and on any kid who might be watching.

Temporarily funny perhaps, but so not worth being referred to as the "Blue Man Group"by two angry and snickering mothers.