A dust particle is floating merrily in the air. All of a sudden, it gets an inclination to enter a human body- an inclination that is furthered by the wind. It spots a big nose (such as mine) and enters freely into it.
Okay, so this might provoke some disgust: imagine the small hair that lines the inside of the nose. It forms the vanguard of the body and tries to impede the movement of the particle. But the particle is strong: it doesn't give up that easy. It swooshes past the hair and charges towards the mucus. The mucus tries to capture the particle, but unfortunately, the particle has the energy of a windmill. Alas, my external defense system fails!
Now my immunity system gets all fired up. It produces an army of IgE antibodies against that dust particle. They engulf the particle, thus freeing my body from any damage. Or so they think. Because the next thing I know, I'm sneezing at a rate that can get me into the Guinness book and stuff is coming out of my nose and flying to places I can't even see!
Seriously? So much trouble for a small dust particle?
Damn my IgE antibodies. They're my least favourite.