Presley’s first No.1 was all about the voice and the rhythm just did the job it had to. “Jailhouse Rock”, his second, is nothing without its beat. The lyrics are funny, of course, and Elvis as skilful as before (his specific trick here is combining a breakneck holler with the pinpoint comic timing the song asks for). But without that tension-racking drum and piano rhythm, half heartbeat half roll, “Jailhouse Rock” would just be a skit. Every time those piano chords hit and linger it’s a promise made to your hips that good things are just seconds away: so much of the fun in dancing (in pop) is rooted in that anticipation.