My dog Jack is very friendly, and he likes to be around people. Yesterday, our neighbors were having a party, and we all went over to cookout and swim at their house. We could hear Jack barking loudly from our backyard. After a little while, he got quiet, so we thought he had finally calmed down. But, several minutes later, all of the adults start laughing, and I see a black blur and hear a giant splash at the other end of the pool. Why was Jack barking?