In an instant, your olfactory epithelium and olfactory nerve worked together to get a message to your olfactory bulb. Once your brain unscrambled the nerve impulses, it recognized the smell as a dangerous one, and you knew to check on your toast. Your brain unscrambled the smell message and you knew it was time to clean things up. When your brain sends a message based on a smell, it's because you've trained your brain to recognize a certain smell. The first time you smelled peanut butter, it was a new smell that your brain had to translate.
Most people just think of the tongue when they think about taste.
The ability to smell and taste go together because odors from foods allow us to taste more fully. Without your sense of smell, the food won't be as tasty the second time around. In fact, some foods are downright hard to taste at all without your sense of smell. You can experiment with different foods to see which ones rely more on smell to let you taste them. And the next time you have to take a liquid medicine that you hate, try holding your nose - you can bet that medicine won't taste quite so gross.