use list to calculate or update fields

I have a list I want to use to update cells in a field. I used SearchCursor to populate a list based on the number:

['Horse', 'Dog']

What I want my table to look like:

Animal Number AnimalNumber
Horse 777 Horse, Dog
Dog 777 Horse, Dog
Cat 999 Cat

I'm stumped. I would like to access my list with row values (ie list[0], list[1]) and use an expression to update/calculate the field but not sure if this the way to go about it.