From And Then There Were None:
Well, he’d enjoy a chat about old times. He’d had a fancy lately that fellows were rather fighting shy of him. All owing to that damned rumour! By God, it was pretty hard—nearly thirty years ago now! Armitage had talked, he supposed. Damned young pup! What did he know about it? Oh, well, no good brooding about these things! One fancied things sometimes—fancied a fellow was looking at you queerly.
I am not able to figure out what the line "One fancied things sometimes—fancied a fellow was looking at you queerly." is trying to say. And why is there a dash in midst of the sentence, also what do these dashes usually mean?