A baby is still crying. Then Waters takes the warning.
The Thin Ice is the second track on The Wall, and it starts before anyone has agreed to sing. The baby cry at the end of In the Flesh? is still in the room. Then Richard Wright’s piano and Hammond organ lay down a soft 6/8, the same family of changes as a doo-wop ballad: C, A minor, F, G. David Gilmour sings the first verse, the first time his voice appears on the album. “Mama loves her baby, and daddy loves you too.” It is a lullaby with the temperature already wrong. Roger Waters wrote the song alone. He does not sing this part.
He takes the second verse himself. The piano goes staccato. “If you should go skating on the thin ice of modern life.” Waters’ bass drops an F sharp against an A minor chord, a note that does not belong, and the polite key does not survive the guitar. Gilmour’s distorted solo abandons the lullaby, holds a C, and crossfades into Another Brick in the Wall, Part 1, with a D minor slipped under the last chord. Two minutes and thirty seconds. The child is already in trouble.
The sessions ran from April to November 1979: Super Bear and Studio Miraval in France, then Cherokee, Producers Workshop and The Village in Los Angeles. Producers: Bob Ezrin, Gilmour, James Guthrie, Waters. Harvest released The Wall in Britain on 30 November 1979 (No. 3). Columbia released it in the United States on 8 December (No. 1). On Waters’ original demo tape the instrumental half had been called Instrumental Theme. A longer eight-bar piano introduction, with Wright’s organ under a Gilmour melody, was cut before release. The 1982 film put some of that piano back and moved the baby cry to Goodbye Blue Sky.
I think it’s about how parents start inducing, almost inject, their own fears and worries into their children from a very early age. Particularly in my case when they had just been through a world war. We all go through devastating experiences and we tend to pass them onto our children when they are very young.
(Roger Waters, interview with Jim Ladd, KLOS, 1979)

On The Wall shows of 1980 and 1981 the song sits between the surrogate band’s opening and the first brick, with Gerald Scarfe’s films already moving. It was never a single. It does not need to be. The lullaby lasts under a minute of singing, and then the record stops pretending the child is safe. Gilmour’s voice is the parent. Waters’ voice is the warning. The guitar is already the next song.
Listen for the join. The last chord of The Thin Ice does not resolve so much as give way, and Another Brick in the Wall, Part 1 is the father’s death in the war, the first real brick. Waters told Jim Ladd the fear was his generation’s, children raised in the shadow of a war their parents had just survived. The ice is the promise that someone will catch you. On this track, it does not hold. Wright’s piano is the last soft sound on this side of the record, and it has already turned staccato before the guitar arrives.