My vet, if you take in 3 or more AT ONE TIME, you get a discount on the office visit part of the bill. It's about 5 dollars off. Once I took 5 cats in (had the appointment made that way). Afterwards, he said if I bring in any more at one time he'd have to reserve the entire day for me!

Now I just take 3 at a time, a mix of dogs and cats works as well for the discount.