How can i can detect a pattern present 2 times in a chain character without specifying the pattern?

I want to select characters chains in which a same combination of characters appears two times. But i can't use grepl because i can't specify the pattern which is different in every characters chain.

Here is an example of what i mean :

Flabellum transversaletransversale

Fungiacyathus pusilluspusillus

i want to detect when this happend and add a space between the same combinations of character.

Thank you for your answer.