Not all antibiotics have that rotten egg smell, but those that do typically contain a Sulfur compound in the form of hydrogen sulfide that gives it that rancid smell.
It’s to brace/strengthen your core. Your body is “smart” enough to realize you’re about to put a lot of strain on your lower spine, so it forces you to contract all the muscles in the area to bolster it. This is why a belt helps deadlifts or squats, it gives something for those muscles to push against, further protecting the spine.
God bless your rice crispys