Spasms may occur frequently and last for several minutes with the body shaped into a characteristic form called opisthotonos.

Torsion of the neck (opisthotonos or torticollis) is observed in severely affected animals.

Back muscle spasms often cause arching, called opisthotonos.

The characteristic position is called "stargazing", meaning a chick "sitting on its hocks and the head in opisthotonos".

Tetanic spasms can occur in a distinctive form called opisthotonos and be sufficiently severe to fracture long bones.

Indeed, feeding the pigeons upon polished rice leads to an easily recognizable behavior of head retraction, a condition called opisthotonos.

Neurological examination showed irritability, opisthotonos, and hypotonia.

Exposed birds exhibited ataxia, wing drop, opisthotonos, immobility, hyperactivity, fluid-filled crops and intestines, and discolored livers.

They may also occur as part of an extrapyramidal adverse drug reaction of some typical antipsychotic drugs, specifically the opisthotonos effect of acute dystonic reaction in which "tetanic" heightening of entire body, head and belly up occurs.

Opisthotonus or opisthotonos, from Greek roots, opistho meaning "behind" and tonos meaning "tension", is a state of severe hyperextension and spasticity in which an individual's head, neck and spinal column enter into a complete "bridging" or "arching" position.

Clinical signs of PEM are variable depending on the area of the cerebral cortex affected and may include head pressing, dullness, opisthotonos, central blindness, anorexia, muscle tremors, teeth grinding, trismus, salivation, drooling, convulsions, nystagmus, clonic convulsions, and recumbency.