大可不必

大 = 一 + 人 : The big (大), huge (大) robot (mnemonic symbol for 大) is working out in the ashram's bathroom (a4). He's lifting a flute (一) to which Don Quixote (d) and Neanderthal man (人) are clinging.

可 = 丁 + 口 : Karl Marx (k) is challenging his abilities (可) in the elevator's living room (e3). He tries to force a nail (丁) into a mandarin (口), just by using his head. On top of that he tries to do so one thousand times, in order to create a bed of nails (mnemonic symbol for 可).

可 = 丁 + 口 : Alternative mnemonic symbol: kebab, from the pronunciation "ke". Karl Marx (k) is preparing a kebab (mnemonic symbol for 可) in the elevator's living room (e3). He also skewers mandarins (口) on the long steel nails (丁) and will only allow (可) his guests to eat the rest of the kebab if they eat their mandarins first.

不 = 丆 + 卜 : Bruno Bear (bu) is setting up a wind wheel (丆) with a voodoo staff (卜) in the space station's bathroom (Ø4). He also puts a "forbidden" sign (mnemonic symbol for 不) on it, to make clear that it may not (不) be stopped.

必 = 丿 + 心 : Mnemonic symbol: 忽必烈 [Hū​bì​liè​], Kublai Khan. Certainly (必) Kublai Khan (必) has to keep face, but he cannot hold it any longer. In the space station's bathroom (Ø4), He absolutely has to (必) tell Brunhilde (bi) his love for her strong character and offers her his heart (心). Brunhilde is a bit embarrassed because all she has to offer in return is a banana (丿). Kublai Khan feels like his heart has been crossed out (the 丿 stroke is crossing out 心 in 必).