Print out, cut out and hand out to each group then have them swap. In each group there is three or so students and one student will start the topic and continue the sentence. A run away train is a conversation that just keeps going and even if the students started a topic it can transform into a completely different topic. Each topic starts with an incomplete sentence and the first student has to continue.

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I believe that living in a small town is much better than living in a large city, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. Watching movies at the cinema is much better than viewing it on TV, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. When I travel I prefer to take the train than an air plane, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I rather eat fast food than cooking at home, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I prefer to stay single all of my life and never marry, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I don't want to ever travel to any other country only visit places in my own country, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I don't want to live for a long time and grow old I think it is better to die young, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I believe working a simple job with a low salary is better than working a difficult job with a higher salary, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I don't care about the environment that I throw rubbish on the ground, because ... (finish this sentence with your own ideas.)

You have to start the conversation and the other students will disagree with your ideas and then you must also disagree with what they say. I think a snake makes a better pet than a dog or a cat, because ... (finish this sentence with your own ideas.)