Provide the theme summaries for the following conversation: 

#Person1#: I was just watching a documentary on TV about how people use dogs for various purpose. It was very interesting.
#Person2#: I love dogs. They have been used as guards for centuries. Nowadays, they are often used to find illegal drugs and bombs by the police and customs officers.
#Person1#: The documentary also pointed out that they are used by shepherds to round up sheep and by rescue workers to find people trapped under rubble or snow.
#Person2#: Horses are useful to people too. We use them for sports and recreation.
#Person1#: Don ' t forget that horses are still used in many countries to pull ploughs and carts.
#Person2#: Can you ride a horse?
#Person1#: Yes, I can. I don ' t ride regularly though. How about you?
#Person2#: I can ride too. Perhaps we could go horse riding together at the weekend?
#Person1#: What a good idea!

Summary: 
#Person1# and #Person2# think dogs and horses are very useful to human, and they find that both of them can ride a horse.