I always thought it was about a mindframe where everything seems perfect, even though it's not - a second of perfect peace in the midst of chaos.

Then, I considered it was about a rockstar suffering from stagefright - and being giving heroin, and then he is no longer scared.

Then, I heard the band said it was about Syd.

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"Don't be surprised, when a crack in the ice Appears under your feet
You slip out of your depth and out of your mind, With your fear flowing out behind you
As you claw the thin ice.." - Pink Floyd, The Thin Ice