Conditional sums based on conditional drop down selections

My excel sheet looks something like this:

Animal | Weight | Date
______________________
Dog 5 Jan/1/2015
Cat 2 Feb/19/2015
Cow 9 Jan/2/2015
Cow 6 Jan/1/2015
Dog 1 Jan/1/2015
Dog 4 March/1/2015


I then would like a to have out like this where the first column is a drop down, the second is a dropdown as well and the third is a total:


Choose Animal | Choose Month | Sum of all the weight
_______________________________________________
[Dog,Cow,Cat] | [Jan - Dec] | [Sum of the animal chosen for that month]


So I would like to choose an animal, then choose a month and it should sum the weight. For example if I chose Dog and Jan the total weight should equal 6 (5+1). I am unsure how to accomplish this as it needs to take the sum from the first section, but the criteria for that section is based on the dropdown values of the the second section (unsure if I can even create dropdowns such as this?)

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PERFECT! Thanks so much EXACTLY what I needed! Your are Batman!