First thought was "thoughts", but the electron synapse reaction time is rather measurable I believe, and so in principle the manifestation of the thought as a set of images (or words or what have you), is most likely O(1).
Perhaps O(0) is things that could have happened, but did not happen?
In C, printf("Hello world.") is an O(1) function (the number of charactes is constant), but in Python, I'm suggesting that it might be O(0) due to Python being designed as a high-level language, where the # of characters isn't considered for computing the function, but as seen as one operation.
That's my take...
That's not what it means / how it works. I'm not much of a mathematician, but O(1) simply means a routine that will always take the same amount of time, regardless the input data.
But what of a call like PRINT 1? It is different than a call like PRINT "How many characters will have to be output", yes? So, I believe there is a meaningful difference to actually make an O(0) designation for the sake of completeness. Thank you. You may be seated. Marxos