I have a certificate to get 2 free tubes when you buy 6 or 1 free tube when you buy 4. Looks like you take it with you to the vet to buy it with your info filled out, then the vet fills out their part and sends it in (not too clear, hopefully you or your vet can figure it out). My cat doesn't go outside except for a few minutes on the balcony here and there, so I don't use anything like this. If anyone wants this I'll be happy to mail it to you. The offer expires Sept 30.