I'm quite familiar with musical notation, but you're right, that's odd and I've never experienced it before.

My absolute best guess would that it's a trill between those two notes. I remember seeing a trill between two notes that weren't right next to eachother on clarinet sheet music, and it wasn't close to what a trill looks like at all. when the notes are farther apart than one note it tends to look weird and convoluted.

I don't want to sound condescending or anything here. My advice is to get an MP3 of that song played originally by it's author or someone who knows what they're doing and listen to that part and see how he plays it. You've probably already tried that, so I don't want to sound condescending here or anything.

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But I'm not the only one; the universal dreamer rises, I hope one day you'll join us; and dream along.