What is certainly a fun example of a booming economy, the National Retail Federation (NRF) says Americans will spend $9 billion celebrating Halloween this year -- with a reported $480 million of that earmarked to pet costumes.

The organization notes that pet costumes represent 15% of the $3.2 billion spent on all costume sales, with an estimated 31 million people expected to buy disguises for their dogs and cats.

What's more, of the nearly 7 thousand consumers polled about their Halloween plans, millennials are the ones who most commonly admit their pets' costumes are important. The trend, the NRF notes, is born out of that age group's use of social media: After all -- you just gotta Insta your dog dressed up as a pumpkin against its will.

The organization ranked the most popular costumes for pets:

1. Pumpkin - 11.2%
2. Hot dog - 7.4%
3. Bumblebee - 4.9%
4. Devil - 3.2%
5. Cat - 3.1%
6. Dog - 3.1%
7. Lion - 2.9%
8. Star Wars character - 2.8%
9. Superhero - 2.7%
10. Ghost - 2.5%