Rust. Anybody? Rust. Anybody? Rust. Anybo...
No need for me to tell you that the rusting of iron requires the presence of water. But whilst trying to find out some interestingly dull info on the goldy orange flakey stuff I was made aware that because rust has higher volume than the originating mass of iron, its buildup may force adjacent parts apart - a phenomenon which is apparently known as 'rust smacking'.
(snap is a pic of the rusty latch on our pretty knackered weathered woodenwonky gate)