Sponges are animals. Mostly they don't move around much once they're grown up (in this way they're not unlike humans) but some sorts of sponges can move at a rate of..ooh, several millimetres a day. If they're roused.
Don't let their slowness lure you into a false sense of security, though, because there are sponges out there that are killers.
Well, they're not at all friendly to shrimps, anyway.
...not only that, but some of them are two metres tall, too.
Most marvellously, some glass sponges deep in the oceans are crowned with optical fibres very like those used in modern telecommunication systems. Glass sponges also may live as long as 23,000 years, too.
These are glass sponges.
The easiest sort of sponge to spot is, obviously, the plastic imitation used for mopping up.
Or you might know a sponger: that's someone who soaks up other people's money by begging and whingeing.
Or if you're lucky you might have a sponge cake. This looks quite like a sea sponge, but contains more sugar and tastes much nicer. Or so I should imagine.
Spot the frippet: sponge. This word has been English since before the Normans arrived, and before that there were Latin and Greek words that were very much the same.