Cover songs are a major part of Metallica's career. Never shy to beat their chest about what bands wielded the most influence on them, they've offered their interpretations of über underground New Wave of British Heavy Metal tracks to timeless classics like Bob Seger's "Turn the Page." To the chagrin of thrashers everywhere, they've never been in bed with their own kind and committed to a full-on thrash cover, which is what makes this footage of Metallica jamming on some Slayer so notable.

The video above was taken from a pre-show rehearsal session in 2009. It's a few seconds before James Hetfield cuts through the noise with the iconic riff to "Raining Blood" and Lars Ulrich quickly comes in with the song's signature bellowing floor tom strikes. It eventually falls apart and then Ulrich chimes in, suggesting the band can play the intro and go into "St. Anger." They muck about for a short while and end the video by playing the Kill 'Em All favorite "Hit the Lights."

Below, we take you back to Hetfield's famed mullet-era. Performing at the Monsters of Rock festival at Castle Donnington in England, Metallica went back a dozen years to Slayer's Show No Mercy debut, tearing off part of "Black Magic." They stop as Papa Het delivers a grunt, then he asks the crowd if they want to hear any Skid Row. They miserably flub their way through a small portion of "Youth Gone Wild" with a cringeworthy vocal from their frontman.

On the "WorldWired" tour, Metallica have taken the jamming to the stage, paying tribute to local musical icons at each stop. In Minnesota earlier this month (September), Rob Trujillo and Kirk Hammett's "Doodle" skit found the two performing a portion of Prince's "When Doves Cry." The band just wrapped up the first round of dates on their second North American tour leg in support of 2016's Hardwired to Self-Destruct and will resume road activities in October with dates scheduled through March of next year. Head here to see them all.