Animals. Sort of. They were setting the album up to be released on the US 8-track tape (remember those?) and needed a bit of music to bridge the two versions of 'Pigs on the Wing.' He was "available" at the time, and recorded a short guitar solo.
8-tracks had (as you might guess) 8 tracks; or 4 stereo tracks. This meant that albums had to be divided up into four roughly equal parts. There's some confusion as to how the tape was arranged (there may be more than one version), but one arrangement was as follows, according to owner Donald Scheidt:
Anyway, regardless of how the Animals 8-track was arranged, we have it on good authority that this is the only Floyd album on which Snowy White appeared. He has also appeared with the Floyd in a couple of tours.