Friend Took Dog To Vet; Who Owes The Bill?

Leo and Rebecca PEEPS COURT!!!! You be the judge! 

I was watching my friend's dog while they were on vacation. Well the dog got sick and I called them to tell them. The dog was throwing up bad and I asked if they wanted me to take the dog to the vet. She said NO do not take him we will be home soon. Well the dog continued to get sick and I did take him to the vet. NOW the dog owner doesn't want to pay the vet bill REALLY??? 

Who do you think should pay the vet bill??