Jack felt compelled to go to the park. He wasn't exactly sure why, or how, and truthfully, he wasn't even giving it any thought. He just sort of... went.
There were others in the park. Many others. So many others that a living Jack, not a reanimated Jack, would have been concerned with what exactly was going on. This Jack didn't ask questions. He moaned a sound that sounded like it could have been a greeting as he joined up with those who were like him.
Gathering. They were gathering. Whatever they were gathering for, Jack didn't know and again, he wasn't giving it any thought. He just sort of did whatever he felt primitively compelled to do.