| Grade 1 |
Loss of posture associated with facial clonus, including chewing, and clonus of forelimbs and/or hindlimbs |
| Grade 2 |
Grade 1 seizure followed by recovery of the righting reflex and low intensity bouncing |
| Grade 3 |
Grade 1 and/or 2 features with recovery of the righting reflex followed by wild running and popcorning |
| Grade 4 |
Grade 3 followed by forelimb and/or hindlimb treading |
| Grade 5 |
Grades 3 and/or 4 followed by bilateral tonic extension of the forelimbs |
| Grade 6 |
Grade 5 followed by bilateral tonic extension of the hindlimbs |
| Grade 7 |
Grade 6 followed by immediate death |
