Floor experts?

[sleepyjeff]

Ok, I don't know if this qualifies for the Egg Head section but here goes:

My house has hardwood floors(original from the late 50s) that seem sound when walked, jumped, skipped, and thundered upon by My Wife, Son, his friends and myself.........but when our little 16 pound Basset/Dashund mix simply trots upon certain sections of the floor it's like a California Earthquake; dishes rattle, drinks slosh, and basically he can make a whole room shake???

We just don't get it.....how can such a little amount of weight make the house shake so much when far greater weights cause no vibrations whatsoever