Yes - meat :D
Seriously though, cats are naturally carnivorous and don't really chew as much as slice (but thats being a bit pedantic) in order to keep their teeth clean.
Eating grass/plant matter helps with digestion but can be overindulged in - especially with house cats, since to them it can be something special/zomg amazing, but you already know that.
If your cats aren't used to eating raw meat, I would start with something soft like pure chicken meat, then maybe offer necks that are already cut in half (again, needs to be raw, cooked bones get brittle). If they master that you can stop cutting the necks in half and move on to halved chicken wings f.e.
Best stuff to clean cat teeth are dense cubes of beef or chicken wings in my opinion. Anything thats a bit harder to separate.
Rules for feeding raw meat:
- For yourself / humans only: The usual rules for handling raw food - and especially meat - apply, so wash your hands after feeding/handling the meat etc.
Preferrably give them their meat in a small, easily cleanable area. They will usually play with it and carry it around, so close the doors first.
Cat muscles can get sore, too - so don't do it too often in the beginning :)
It is not uncommon for them to require smaller pieces of meat at the beginning as they're simply not used to separating large pieces of meat (or 'worse', cracking bones). Adjust to their pace.
In general, don't give them raw meat more often than about once every 2 weeks. If you want to give them raw meat more often, you need to supplement it properly (it's not the same/as easy as raw-feeding dogs and a lot to read up on, but can be worth it) or they might get sick long-term.
Growling and 'hiding' meat is normal - thats why a small closed room is recommended :)