It's not a round ball, made of very soft latex with a squeaker, it fits perfectly in their mouth. I bought a set of 6 in a pkg. I forget what I paid but it wasn't much.
Walmart has them, a set of 3 for $2.72
www.walmart.com/ip/Vibrant-Life-Playful-Buddy-Emoticon-Dog-Chew-Toy-Chew-Level-2-3-Count/183907365