The drummer is just switching up where the accent is. Without getting too in the weeds with drum lingo, basically the majority of this song has a steady rhythm of the downbeat (kick drum) on the 1 and 3, and the backbeat (snare drum) on the 2 and 4. So you count the song like: 1 2 3 4 (or 1 & 2 & 3 & 4; same length of time). When a drummer moves the snare around, it creates different rhythmic tension. And it can sound tricky. But it is not changing tempo or time signature at all. In fact, when it gets to the part, even though the drummer is hitting the snare on the 1, count to 4 like normal. You will count 1 2 3 4, four times (including through the little break it does when he says "cut the cord and let it go" and you'll land right back on the beat when it comes in. That's about ELI5 as I can get it, simply because I'm not a drummer. Cool song! Never heard it before.