I've noticed this too. If you have a dog, you also learn very quickly just how many discarded chicken bones exist throughout the city (hint: it's more than you want it to be).
I completely agree. I clean up with Emin and rubbish, and this project was initially inspired because I have a corgi vacuum cleaner who eats everything on the ground. Once I started scanning, it's impossible to unsee the litter. So we started cleaning and recording it!