Rice cereal is nasty. Have you smelled it? Unless you have a huge history of food allergies, try something else. Baby food oatmeal is way better than rice cereal. Or mix the rice cereal with some apple sauce. My boys' favorite was warm baby oatmeal with applesauce and a dash of cinnamon. Or baby peaches instead of the oatmeal. I even tasted it! The first tastes like apple crisp and the second like peach cobbler. Mmmm!
Or try plain old' applesauce or another baby food.
The reflex that makes babies spit things out is almost always gone by 4 months, and doesn't explain the "making a face" so I seriously doubt that's what it is. Sure, now they say to wait until 6 months, but my pediatrician asked me what I do, instead of telling me what to do, because frankly, my kids can't handle waiting until 6 months. They're ravenous and are eating every 1 hour at 3 1/2 months. Do what you know is right for your baby. And trying to teach him how to eat solids doesn't have to be about getting more food down him. It can be just teaching him to eat. So even if he doesn't get a significant amount of solids until he's 6 months old, you can still start practicing with him.
Besides, they used to start babies on solids at 3 months. Then it was 4 months when I had my first two kids (they're 6 and 4, so it wasn't that long ago) and they said NOT to wait until 6 months or later because "studies showed" that kids who waited that long often refused to begin solids and had a significantly lower food palette (read: picky eaters.) But apparently that's all out the window just between my two youngest kids (ages 4 and 9 months) because everything's changed. Now it's 6 months? If the experts don't really know, then what does it really matter if you start at 5 months instead of 6? I'm not saying that we should ignore professional advice, but COME ON. Conflicting studies are published every single day. Go with your Mother's Intuition. That's what three kids have taught me.