Literally Laughing One's Head Off

The dinner party was in full swing. Suzie's guests had finished their starters when Nigel decided to tell his tasteless, crass joke about a missing girl. Silence. Broken only by the Lionel Ritchie CD on the stereo.
Stefan, the Cambridge graduate who worked in Suzie's department, was the only one to laugh.
As he became more hysterical, he threw his head back.
His neck seemed to tear, and his laughter ceased as his head came away and thudded to the floor.
It rolled across the carpet irregularly, coming to rest against the sideboard.

Lionel continued singing 'Dancing on the Ceiling'.