Certain songs are instantly recognizable from the moment they kick in. Whether it's an earworm riff, an unforgettable vocal or some other extraordinary sound, there's something special about those rock and metal songs that you can always recognize straight away. Plenty of these sorts of tracks are smash hits and the kinds of songs bands are best known for, but so too can they be deep cuts that just have that effervescent quality that get a live audience hyped as soon as the band starts playing. Iconic intros come in all shapes and sizes, and below you'll find 30 examples we've chosen from the 1990s — a decade ruled by the likes of Nirvana, Alice in Chains and Green Day — of rock and metal songs you'll always recognize from the first few notes.