次聲波

次 = 冫 + 欠 : Mnemonic symbol: the cube, as in words involving 三次 relate to "cubic equations" or "cube (third power)". The King of Chu (c) pulls a popsicle (冫) out of the cube (次) in the space station's bathroom (Ø4) and leaves an IOU note (欠) on the cube.

声 = 士 + 尸 + 丨 : Sherlock Holmes (sh) hears the terrifying sound (声) of bone (丨) on stone in front of the engine ((e)ng1), and he's sure that there must be a ghost (尸). Indeed it's only the bachelor (士) who wants to scare Sherlock.

波 = 氵 + 皮 : Before entering observatory every visitor has to take off their shoes, so there are a lot of leather shoes (皮) in front of the observatory (o1). Beelzebub (b) cannot miss the opportunity to make a huge wave (波) by pouring his water bottle (氵) and to flush away all the shoes.

波 = 氵 + 皮 : Before entering observatory every visitor has to take off their shoes, so there are a lot of leather shoes (皮) in front of the observatory (o1). Beelzebub (b) cannot miss the opportunity to make a huge wave (波) by pouring his water bottle (氵) and to flush away all the shoes.