we started with taking it out of zebs mounth and "dropping" it on the floor, Hes very very good even to the point now we can give him a treat he can be half chewing it and if we say drop he does Hes 20weeks
It doesnt take him and making sure you do each time, but they do cotton on!

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Owner to-
lots of rodents
2 monster dogs
1 slinky cat