When someone says "Trick or Treat," there are many ways to respond. Here are some options:

• Keep it simple: Smile and say "Happy Halloween" or "Hello".
• Compliment their costume: Say "Wow, great costumes!" or "Your costume looks great".
• Act scared: Pretend to be scared and say "You scared me!" or "Spooky!".
• Offer candy: Say "Here you go!" or "Have some treats!".
• Engage in small talk: Ask "What are you supposed to be?" or "How is your Halloween going?".

Remember, the most important thing is to be friendly and welcoming to the trick-or-treaters.