The PetSafe® Spray Refill cartridges are easy to replace with no mess. Simply remove the empty cartridge and replace with the new one. The citronella scent is harmless to your dog and is meant to act as a distraction to help stop nuisance barking. The PetSafe® Spray Refill cartridge is 100% recyclable and safe for you and your dog! Your pet deserves the best. Trust PetSafe® to help keep your pet healthy, safe and happy.