There is a creature sitting on my lawn.

There is? But I don’t see a thing.

Of course not. The creature is invisible. You can’t see it with your naked eyes nor can it be detected with any sort of optical equipment.

But I don’t hear anything of it either.

Of course not, the creature never makes a sound.

Well, then, what kind of creature is it?

It’s a rather large creature, about six feet tall and two feet wide.

Well then, if it’s that large I should be able to go outside and feel around for it until I find it.

No, that’s quite impossible. The creature lacks all mass whatsoever. You wouldn’t be able to feel it nor would you be able to detect it with any sort of seismic sensor or even a statistical analysis of the movements of air particles in the area.

Ah, it must be one of those new-fangled energy creatures. Let me get out my magnetometer.

Don’t bother.

How in the world am I supposed to detect this creature?

Oh that’s quite impossible. The creature is completely undetectable by any scientific instrument or method now or that will ever be made.

How can you possibly know about it then?

It talks to me.