I found an interesting article about things that happen in the studio while recording, but still end up in the mix. This is one of them..
The mysterious piano chord heard at 0:04 is an unusual, atonal cluster that has nothing to do with the rest of the song. So what gives? Well it turns out Sting slinked back to relax on a nearby piano but didn’t realize the lid was up, so he unwittingly played that gloriously dissonant chord with his butt. This also explains his laugh at 0:06.