barnacle bur color flower green plant pointed sharp sharp-pointed sky spike thistle thorn tip yellow Australian bird black-winged blue-black carnivore carnivorous crest crested egretta-picata Heron long-legged pied-egret Pied-Heron pond reeds reedy reflections sharp-beaked sharp-bill sharp-eyed thin wader wading wading-bird water yellow-bill yellow-legged aggressive alert common gymnorhina tibicen insectivore lookout Magpie protective sharp eyed swoop swooping territorial watchful watching Bin caution contain container containment contaminated contamination danger dangerous disposable disposal hospital hospital-objects infectious medical needles sanitation sharps special substances syringes used angles black and white buildings city corners glass high rise linear modern sharp corners Singapore straight up and down walls windows appearance barbed-tape barbed-wire barbs barricade barrier double fence fencing gray grey injury metal protection razor-sharp razor-wire restraint security security-fence silvery spirals strands twists warning wire abstract angled architectural architecture building contemporary contrast contrasting distinctive edged edges elements exterior external framed frames geometric geometric-shapes height high high-rise light lines patterned patterns perspectives sharp-cornered sharp-corners straight-up-and-down surface surfaces textured textures views wall