sit up (and take notice)

(口)吃惊，吓一跳；警觉

siphon, sir, sire, siren, sirloin, sirocco, sirup, sisal, sissy (also cissy), sister, sister-in-law, sisterhood, sisterly, sit, sit down, sit down on, sit for, sit in, sit on, sit up, sit-down, sit-in, sitar, sitcom, site, sitter, sitting, sitting member, sitting tenant, sitting-room, situate, situated, situation, situation comedy, situational, six, six-footer, six-pack, six-shooter, sixfold,