Related Clues:

• Answers
• Does a double take, e.g.
• Responds to stimuli
• Responds to a stimulus
• Does a double-take
• Changes chemically
• Gasps, perhaps
• Isn't passive
• Strikes back
• Undergoes a chemical change
• Flinches, perhaps
• Does a spit-take, e.g.
• Responds
• Does a knee jerk, e.g.
• Looks shocked, e.g.