Of course any appearance by Taylor Swift on the Ellen DeGeneres show is going to be really likable, juuuust short of it getting saccharine, and you imagine Zac Efron wouldn't make things too belligerent either. And of course a violence-free, personalized cover of Foster the People's "Pumped Up Kicks" will get likes from lots of people; the song choice even fits Taylor Swift's duet criteria of late, because the show's filmed in L.A.
Here, then, are some things you might learn from the video below: Taylor Swift has guitar picks with her face on them and is willing to give guitar lessons to people who appear with her on Ellen. She also does an excellent job of being super-impressed by one strum. Zac Efron, meanwhile, is probably at least four years older than you think by now and is excellent at either improvising lyrics on the spot or a couple hours beforehand. She's aware of what questions she gets asked too much in interviews; he's aware of the vibe he brings places. Both of them are probably well aware of how many millions of hits on YouTube this is going to get them.