When all judgment "this is great" or "this sucks" has dropped aside and there's just the experience, whatever it is, and no part of the brain is analyzing it.
For an example, sometimes on a walk in the park something enters the foreground of attention, let's say "it" is a "flower". But, in "perfect moments", "I" am not "observing" a "flower". It's all a unitary experience without the illusions created by analyzing it (and by illusions I mean the divisions that get added after-the-fact, which are denoted here with quote marks).
Then I think (such a tragic thing sometimes, haha) "That's a lovely flower" and snap! in an instant "the perfect moment" is gone (or rather, it appears into conception, as a memory). "I" exists again. "Observing" is the insipid thing that's replaced the unity, and the "flower" is an "it" getting judged as "lovely". It's then "the perfect moment" may be opined about and described like a stuffed animal in a glass case as I'm doing now.