"Those that that ~"

I have a sentence that I can't grammatically understand. That's the following.
"In doing this he eliminated some more of the acorns, discarding the smaller ones and those that that showed even the slightest crack."
The problem I have is the "those that that".

I know the term "those that," and I think the "those" in this sentence is one of the objects of the "discarding."
Which is to say "discarding the smaller ones, and discarding those that ~."
However, I can't understand why this sentence have two that's in a row.
Can't we say "~ and those that showed~ "?

Could someone please give me a grammatical explanation?