The Kedushah, part of the chazan's repetition of the Amidah, is built around biblical verses in which angels are heard praising God's holiness. The first verse is from Isaiah 6:3 where the prophet overhears the angels declaring "Holy, holy, holy is the Lord of Hosts" and the second is from Ezekiel 3:12 "Blessed is the glory of the Lord from His place".
It's an ancient custom to spring up and down on one's heels while saying these verses (and also a third verse from Psalms 146:10). Many have the practice to bounce on each mention of the word kadosh, "holy". Rabbi Ovadia Yosef, the late Sephardi Chief Rabbi of Israel, held that you should spring up and down three times at each kadosh. Menachem Hameiri, the medieval authority, explains that the reason is to enact our striving upwards towards holiness like angels each time we pronounce the word "holy".