So, I never realized that parrots are as smart as they are. Apparently, a parrot has been shown to possibly understand the concept of 'zero'. That's pretty amazing considering you're dealing with an animal with a brain the size of a walnut.
The other interesting thing is just how hard the concept of zero is. Kids don't get it until around age 4 and many of our ancestors didn't have a word for it until the 1600's. Cool to think that with a bit of calculus, we can now handle indeterminate forms, infinity, and zero functions.