it took me more than a season. people kept telling me you either have it and love it or get hurt so much you quit trying to slide them. I'd always get intimidated, fall back, and slam my hip on the rail. It just took getting comfortable sliding a box, then a small, wide, flat rail to build my confidence and do everything right so I wouldn't bang my hip.
I was feeling real good a few days ago because I could do all the flat rails in our park (about 6 or 7) and then fell on my ribs and bruised them (hopefully they're not broken). Now that I know I can do them, I'm hooked for life. I've started wearing a mouth guard because I've heard horror stories of kids getting their teeth knocked out on rails. They can be a bitch but once you can slide them, there's hardly anything that can be so much fun when the snow is shitty.
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If male strippers were paid as much female ones, I'd be a rich man