If you get some brewers yeast ( I purchase the large bags at Sam's Club they are 1 lb. bags ).
What you do is depending on the size of the animal.
Our dog is 18 lbs. so every day I put 1/2 teaspoon in ice cream for her to eat.
The cat I put 1 pinch in her food each day. It keeps fleas off of them. Fleas don't like the smell of the animal.
But you have to make sure you have the fleas out of the bedding and you carpets and house. This work great and we have not had a fleas on our 3 animals in 4 years.
This is much cheaper then frontline and the animals will not be mad at you .
Good luck