The Ruwak-ruwak is a kind of Heron whose nest if discovered would give the possessor the power of becoming invisible (alimun). But as neither nest nor eggs can usually be found it is held to be childless. Yet, however, if it is possible to approach sufficiently near, when the bird is heard calling in the swamps, it may be seen dipping a twig or else its bent leg into the water, and accompanying its action with its call, as if it were bathing a child on its knee; hence the Malay who hears its note says mockingly, "the Ruwak-ruwak is bathing its young one." Tukang is the name given in Kedah to a kind of Hornbill, which is believed to be the same as the langlin of Perak. The horn is of a yellow tinge, and is made into buttons, which, the Malays say, turn to a livid colour whenever the wearer is about to fall sick, and black when he is threatened by the approach of poison. [243] The Merbu (? merbok) is a variety of Dove which brings good luck to its owner. Instances have been known where all the houses in a village have been burnt except that which contained a merbu; indeed, treatises have been written on the subject of keeping them. When the merbu dies its body merely shrivels up instead of breeding worms, which, it is added, would be worth keeping as curiosities should any appear. [244] The bird called Pedrudang is a diver which has the power of remaining under water for a very long time. It is only to be found where the fish called kelesah exist in large quantities. The eggs of the kelesah are of great size, and the Malays say, therefore, that it cohabits with the pedrudang. These eggs are considered a delicacy by the Malays, who make them into a sort of custard pudding (s'ri-kaya).