Top: plant 艹, bottom: promise, treaty 约 (The thread 糹/糸 at the ladle 勺 reminds to the promise.)
This plant gives the promise to be: medicine.

Left: thread 纟/糸, right: ladle 勺
The thread at the ladle reminds to the contract.

Left: mouth 口, right: contract, agreement 约 (The thread 纟 at the ladle 勺 reminds to the contract.)
The mouth can (according to its contract) say "Oh!"