A Spasm was a type of magical attack. It was a violent expulsion of energy, green-gray in color, that could be employed by either magicians or spirits. It was generally not fatal when used on a person or spirit, though it could cause some damage and could easily shatter objects.
John Mandrake once used a Spasm against his door guard when it attempted to joke with him when he was in a bad mood. When Bartimaeus expressed to Nouda that he wished nothing more than to return to The Other Place, rather than join the revolt of the spirits, Nouda called it an odd decision and Faquarl stated that Bartimaeus was perverse and should be destroyed with a Spasm. Nouda, unhappy with Faquarl's advice, stated that Bartimaeus was free to go.