What's a Lock, Harry?

i've not been back for two and a half years. i can imagine that you guys are picking up the sounds around our voices, and it's, to me, incredibly english. Took a little selpy, didn't we? We're going over a canal right now, and there's a lovely lock. What's a lock, harry? Some kind of gate barrier thing where they am let boats through. And they change the height of the water ton't ow exactly, so yo can go up and down hill. It's amazing how they do that. But we were just thinking about, you know, in a month's time, it'll be april. What