Google Spreadsheet formula

I need a formula for my google spreadsheet. 

I have a drop down list with "Dog", "Cat", "Rat" and "Bat". If I am selecting "Dog" in the next column I would like to get another drop down list which is related to "dog" - "Kennel", "Choke chain", "Puppy Pedigree".  

I requesting the equation for the same... Please help me...

Thank you