it is traditionally the belief of policemen that they can tell what a substance is by sniffing it and then gingerly tasting it , but this practice had ceased in the watch ever since constable flint had dipped his finger into a blackmarket consignment of ammonium chloride cut with radium , said 'yes , this is definitely slab wurble wurble sclup , and had to spend three days tied to his bed until the spiders went away .