The Enterprise receives a distress call from the Vulcan ship Seleya where T'Pol had served before going to Earth, but there are asteroids with random movements in her way. Archer, T'Pol, Reed and Corporal Hawkins get Shuttlepod One to reach Seleya, but they are attacked by the Vulcan survivors that act like zombies and seal the bulkheads, and the rescue team is not able to return to their docked vehicle. When T'Pol feels that she is being also affected in the Seleya, she transmits the data she had obtained to Dr. Phlox for analysis. Dr. Phlox finds that a toxin in the Trellium causes brain damage in the Vulcans and T'Pol has to immediately return to the Enterprise for treatment. However, Shuttlepod Two needs to be repaired after an unsuccessful trial of Trip and Travis of bringing Trellium ore from one asteroid to be refined.
"Impulse" is a tense episode with great performance of Jolene Blalock when her character becomes paranoid and incapable of controlling her emotions. The Vulcan survivors look like zombies, returning to the primitive status of violent race. My vote is eight.
Title (Brazil): "Impulso" ("Impulse")