That can also be ternary

I don’t get Gray Code, I never heard of it, and yet the joke isn’t lost on me.

@Background Pony
 
Can you not count?
 

fail…  
if it was grey code, 10 would be 3, not 2

Haha, oh Cheerilee.  
I got it, by the way.

The practical point of a Gray Code is to enumerate states in a finite state machine in such a way that only one bit changes per consecutive state transition, thereby saving power from state switching and avoiding potential timing issues in a circuit. Furthermore, they are used to label input vector axes in Karnaugh maps. As such, this is basically an electric engineering joke, although there are pure mathematical applications mentioned in the Wiki article, too.
 
Note there are multiple Gray Codes possible other than the standard reflective binary.

ah dun’ geddit.