Metallica have turned an in-concert improvisation into one of the most beloved parts of their live shows. Since the WorldWired tour began in 2016, bassist Rob Trujillo and guitarist Kirk Hammett have performed a nightly jam known as the "Doodle", and from 2017 onwards this evolved into a tradition of covering a song local to whichever city they are playing. The covers are deliberately rough and ready — the parts are learned shortly before the show and Rob often reads lyrics, frequently in a foreign language, from a music stand — yet the segment has become a highly anticipated highlight that celebrates each host city.

The tradition began in Amsterdam in the summer of 2017 with a ragged take on Golden Earring's Radar Love, and has since spanned everything from When Doves Cry in Minneapolis (a tribute to Prince), Abba's Dancing Queen in Stockholm and Iron Maiden's Killers in London, to more obscure local picks such as Indianapolis punks Zero Boys and Portugal's Xutos & Pontapés. Results vary: a version of The Stone Roses' I Wanna Be Adored in Manchester in 2019 was widely panned, and their Zurich cover of Celtic Frost's The Usurper drew an angry rebuke from frontman Tom G. Warrior, who accused them of "butchering" it. For the M72 tour's no-repeat weekends the pair initially added self-composed Doodles, but these were dropped for the final 2026 leg in favour of local choices, with Eastern European picks — such as the Czech comedy folk song Jožin Z Bažin in Prague — often proving the biggest crowd-pleasers.