Yes the vomitting reflex is to remove the contents of your stomach from your body. You can vomit for a number of reasons: nausea, food poisoning, gastritis, overeating, motion sickness, drug reaction, migraine and infectious diseases like flu.
Some people can make themselves sick by putting their fingers to the back of their throat. This causes a gagging reflex which can lead to vomitting.
Ugh butter with cornflakes doesn’t sound good! My puppy ate a packet of butter once because I had forgotten I’d left it on the table and he snaffled it – he wasn’t sick but he couldn’t eat his dinner that night, and strangely it made the lounge smell like popcorn!