Now it’s this latter muscle that’s involuntary, so the crows feet smile is considered the real spontaneous emotion and is known now as the Duchenne smile.

They were also strapped into a giant centrifuge, where they had to read signals and answer questions despite dizziness, muscle contortions and involuntary spurts of tears.

Seizures can vary from the briefest lapses of attention or muscle jerks, to severe and prolonged convulsions (i.e. violent and involuntary contractions, or a series of contractions, of the muscles).