I saw this on the website for my Agility facility, thought I'd share.
Product alert! There are tennis balls made by Tretorn called "Tretorn X"
that contain an inert substance which presumably helps with the bounce.
However, when the dog pops open the tennis ball while chewing, the
substance makes a terrible gooey mess in
their mouth and presents an aspiration hazard. I was made aware of this
by a client who's dog had a bad experience with just such a tennis
ball. Here is a picture of one exposing the material inside.It seems
that the material is non-toxic. However, it still presents a potential
injury problem. Make your friends aware!
https://sphotos.xx.fbcdn.net/hphotos-snc7/c88.0.403.403/p403x403/480878_216358795140338_1478406168_n.jpg
Hmm the pic is not showing BUT if you copy paste that link above you can see the tennis ball, slit open, to see the 'stuff' inside.