THE DIFFERENCE BETWEEN XXI

What's the difference between:

1. The Blob and Emerald City?
2. A pack animal and a Mexican food staple?
3. A playing card and check-writing fraud?
4. Aahs and Maas?

Answers:

1. Ooze and Oz
2. IT - Burro and burrito
3. IT - King and kiting
4. Cheap thrills and sheep trills

Credit #1: 
Cathy Allis Millhauser