臼(jiu) is mortar and the Chinese character looks exactly like a real stone mortar with which you can smash garlic into pieces!
稻（dao）is rice or rice-plant. What is the top part of 舀（yao)? Experts say it is big ladle with which you get rice-grain from the mortar! -------Maybe！ But I think it is more likely the pestle with which you strike the rice-fruits in the mortar to husk rice! ---------Only in this way, the following explaining would sound reasonable!:
蹈 (dao) --------Dance with feet！The first part of 蹈 is 足，the last character looks like one person is walking with the right foot overtaking the left one! (口 is mouth that represents ‘a man’.)--------So 足 is ‘foot’ in Chinese. --------Then it is easy to understand 蹈！--------------Your feet act as 'pestle’ striking 'mortar' when you are husking rice! ---------That repeating action seems like dance that should not go with too much strength！