So, is that a lot? Let’s assume a very simple model, with Reddit writers picking words from a fixed distribution, 10 words per reply, and all ‘over 1,000 comments’ threads having exactly 1000 comments.

Then, if the probability of picking ‘fried rice’ is p, the probability of ‘fried rice’ not appearing in that 1,000 comment, 10,000 word thread is

  (1-p)^10000

That apparently, is around 0.22:

  (1-p)^10000 = 0.22

Solving for p gives us

  10000 log(1-p) = log(.22)

  log(1-p) = log(.22)/10000

  1-p = exp(log(.22)/10000)

  p = 1 - exp(log(.22)/10000)

That’s about 0.000066, or 1 in 15,000.

Let’s compare that with https://books.google.com/ngrams/graph?content=nazi&year_star....

That gives us numbers close to 0.000066, but only for the mid 1940’s. Current level is around 0.000008 or 1 in 125,000. Let’s compute how many words such a long Reddit thread needs to get at that level:

  (1-0.000008)^w = 0.22

  w log(1-0.000008) = log(0.22)

  w = log(0.22)/log(1-0.000008)

That gives me around 190.000 words. That does not seem impossible for me. If long threads on average have 2,500 comments, it is only 36 words per comment. One would have to look at the distribution of thread length and #words/comment to say more about this.

Now, let’s hope there isn’t an embarrassing error in the above computations :-)