The sponge is possibly the grossest thing in your house. I say this as someone who regularly comes home from holding a train pole and immediately eats finger food (it's builds character!), but still the sponge disgusts me. It is, by nature, a festering cesspool of germs, a wet thing used to clean dirty things that you let fester in the open while also sucking up all the bacteria in the air. The smell of a dirty sponge is one of the worst household odours, one that lingers on your fingers and leads to me obsessively washing my hands after every single sponge contact. It's like cat urine or black mildew - it's the smell of bad housekeeping.