The penalties for assaults become more severe the more serious the injury and the more dangerous the weapon used.
For example, breaking someone's nose with a fist is a misdemeanor, while breaking someone's nose with a bat is a felony because a bat is considered a dangerous instrument. But what else is a dangerous instrument? New York Penal Law Section 10.00(13) says it could be anything. What matters is how it was used.
Some examples of dangerous instruments:
Handkerchief - People v. Cwikla, 46 NY2d 434 (1979) - The victim was gagged with one, which led to death by asphyxiation.
Sidewalk - People v. Galvin, 65 NY2d 761 (1985) - A bar fight where the defendant bounced the victim's head off the sidewalk, causing serious physical injuries.
Garbage bag - People v. Abreu, 283 AD2d 194 (1st Dept.) - Defendant used a garbage bag to choke the victim
Footwear - People v. Carter, 53 NY2d 113 (1981) - Defendant stomped the victim in the face with rubber boots. The boots caused more serious injuries than what we would expect with bare feet. People v. Lappard, 215 AD2d 245 (1st Dept.) and People v. Lev, 33 AD3d 362 (1st Dept. 2006) say sneakers are dangerous instruments. Work Boots? Yes under People v. Elijah B., 28 AD3d 312 (1st Dept.). Plastic sandals? Of course, People v. Byrd, 51 Ad3d 267 (1st Dept.).
Braided Belt - People v. Curtis, 222 AD2d 237 (1st Dept.)
Flyswatter Handle - When used to assault a five year old child - People v. Wade, 232 AD2d 290 (1st Dept. 1996)
TV Remote - People v. Krotoszynski,43 AD3d 450
Human teeth - People v. Owusu, 93 NY2d 398 (1999). Unless they are sharpened or altered by the defendant to make them more dangerous.
Saliva containing HIV - People v. Plunkett, 19 NY3d 400 (2012) - Since the saliva is part of a person, it cannot be considered a dangerous instrument. Dangerous instruments are items that someone uses other than their body parts to cause injury.
Many thanks to a former boss for compiling this list!