What's Your Last Name?

This summer I've been trying to teach Brogan random things he'll need to know sometime in the next year: recognizing how he feels in situations (was that scary or fun?), shapes, state and country flags, holding his crayons correctly, writing out his letters, telling me how many objects he has, his last name, ect.
The changes in him this summer have been fun to witness and be a part of. It's like I'm discovering a new Brogan every other week.
Just the other day we were at the pool and he asked if he could go down the "dark" slide (it's enclosed from top to bottom). I encouraged him to go for it and waited for him at the bottom. The first time I let Rhiannon go down the dark slide I could hear her screaming from about 2 feet into the tunnel all the way down. She has never gone on it again. So I was interested to see what he'd do. He's not scared of the dark, in fact, he often shuts himself into small, dark places with all his bedding and plays there for quite some time. But this situation is obviously different. So I see him head down, hear no screaming or thrashing and catch him as he swims over to me after he's thrust out the end. I look him over, he's slightly wide eyed, but no other expression graces his face. So I ask, "Was that scary or fun Brogan?" His immediate response? "Scary!" Me, curious, "So do you want to do it again?" Brogan, "Nnnnno!" Okay, so no enclosed water slides. Gotcha.
The funniest thing though, is trying to teach him his last name. I am not sure if he's messing with me or if he doesn't really get it. Cause when I just ask him his name, he'll say, "Brogan Wesley Crabb". But when I ask him what his last name is, he'll invariably say Lobster, Lizard, Tiger ... anything but Crabb. I get it. His last name is also a crustacean. So maybe he thinks they are interchangeable. Any animal will do.