From Longman Dictionary of Contemporary Englishfasten on/upon something phrasal verbATTENTIONto give particular attention to something because you think it is important or interesting My mother fastened on the word ‘unsafe’. → fasten→ See Verb table
Examples from the Corpus
fasten on/upon • What on earth was she now what trend or fad was she fastening on?• But by the spring of 1978 the war was over, and Snyder had fastened on a new cause: the homeless.• These will be fastened on and above them a platform.• An eddy of chill air swirled into the carriage, fastening on his knuckles.• It fastened on Mala like a grasping hand and snatched her into the air.• There are sections of Hazlitt's critical work which fasten on more general issues.• A pounce, the cheetah's jaws fasten on the gazelle's throat, and it is quickly throttled to death.• Then he fastened on the particular problem of coffee. 