The only time you should try to make your dog vomit with hydrogen peroxide is if you know they have swallowed something that is harmful if swallowed. You should contact the vet in order to determine the best way to handle this kind of situation. Be sure to follow there advice to the letter. Keep the dog in a secure enclosed like the bathroom, kitchen or laundry room. Get another person to help you hold the dog, when you give them the peroxide. With a small dog only a capful is needed and 2 tablespoons for a large dog. A syringe may be the best tool to use to get the solution down the dogs throat. Wait quietly while they vomit, it can take as much as 5min. Look at the vomit for anything dangerous that was expelled or looks like something that should not have been swallowed. If nothing substantial comes up repeat.