Single hole in all of my red radishes, why?

Hello everyone!
This is my first post here in this group. The last vegetable garden that I planted here in Honolulu, HI was when I was a little boy around 30 years ago.
Now, I am 37 years old and decided for the fun of reliving old memories, I planted some roma tomatoes, bok choi, mustard cabbage, white stemmed cabbage, long eggplant and the reason for my post, red radishes.
I don't care for red radishes, but I read somewhere that they were easy to grow and fast to mature and make an excellent morale builder, since they develop rapidly, so I figured that if everything else failed, at least I would have a good chance of success with red radishes.
Perhaps it's not a problem, but all my radishes that I pull up to look at have a single small hole about 1mm wide and goes into the body of the radish about a 1/4th of an inch. I cut the radish apart, but I can't find anything in there. At the end of the tube, I see a little brown stuff, but nothing identifiable. Otherwise, the hole and the tube is clean!
Is this a natural forming occurence? I figure that it may be, since if it were a bug or worm or something, wouldn't there be more than only one hole in each radish? I don't think insects would only alot themselves one hole per radish.
Can anyone give me a clue as to these mysterious holes?
For my first time here, I find this group quite interesting.
Thanks!
Kelcey
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Yes, absolutely they are normal for certain varieties, particularly the Divine cultivars, otherwise known as Holey Radishes.
j/k, I don't know what they are. :-)
- S
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