With all the gang muggings on the CTA and in downtown Chicago, I decided last year to carry pepper spray—police-strength in the family-size canister. It shoots a gloppy, yellow stream up to 20 feet. It's surprisingly easy to a hit a target.
I've never had to use it, and wouldn't use it for anything but a genuine emergency, but in testing it, I managed to touch my face with what must have been a minuscule amount of residue that invisibly ended up on the can. It's brutally painful, and left me stinging for 20 minutes. That's why it will stop a bear. The police use a large trigger attachment that probably keeps the residue off their fingers.
My little encounter with the residue made it clear to me that spraying that goo on the peaceful UC Davis protesters was an outrageous act. It's hard to believe those cops were so cavalier about it.