within / among / in / middle / center / while (doing sth) / during / (dialect) OK / all right
中
=
丨
+
口
:
Mnemonic symbol: a dart board, because you always try to hit the center.
Julian Giant Squid (zhu-) is throwing dinosaur bones (丨) as darts on a dart board in front of the engine ((e)ng1). To make it a bit more difficult he's throwing mandarins (口) into the air as well and skewers them up right in the center (中 is a mandarin skewered on a dinosaur bone) in mid flight with the dinosaur bones. He's still able to consistently hit the center (中) of the dart board.
to introduce / to lie between / between / shell / armor
介
=
人
+
丿
+
丨
:
Mnemonic symbol: 介 looks like a rocket 🚀. Neanderthal Man (人) and Joan of Arc (ji) are preparing a rocket (介) for its start. Between (介) the layers of the outer shell (介) they are stuffing bananas (丿) and dinosaur bones (丨).