It's a pretty decent chunk of power down a POTS cable too, as it was designed to ring multiple big chunky metal bells in the days of yore.

I was wiring in a phone extension for my grandma once as a boy and grabbed the live cable instead of the extension and stripped the wire with my teeth (as you do). I've been electrocuted a great number of times by the mains AC, but getting hit by that juicy DC was the best one yet. Jumped me 6ft across the room :D

I discovered the same exact thing wiring a second phone line to my bedroom as a teenager. I jumped into a pile of fiberglass insulation! :/

The teeth. Yikes! But yeah, I remember having the rotary phone disassembled and touching the wires adjusting something when a ring came. Gave me enough of a jolt to remember.