Is the input Bl lu ur rr ry?

Retina, 14 bytes

a`.((.) \2)*.|

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a forces the match to be on the entire string

.((.) \2)*. just means any character (.) followed by a captured group repeated 0 to many times ((...)*) of any character saved into a second captured group ((.)) followed by a space and the same character that was matched in the second capture group (\2). The final . just matches the last character

| allows the empty string to match by having an alternative match of the empty string

Python 3, 60 54 bytes

-6 bytes thanks to Surculose Sputum!

while b:x,y,z,*b=b;x[x!=z][y>' ']

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By using different sets of errors for truthy/falsy inputs this can be 52 bytes, as suggested by Surculose Sputum.

Python 2, 57 bytes

lambda x:x==''.join(c+' '+c for c in x[::3]+x[-1:])[2:-2]

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Uses the same approach as my Pyth answer. The blurring portion of the code is based off of @Surculose Sputum's answer to the original "Blur a string" challenge.