yes and no. i dont think its the tail alone that tells you what is going on with kitty, but the whole body together. i have one little lady who loves to lay down across my chest and doesnt like to be moved. she will lay there purring away, yet her tail is twitching. i think maybe she is anticipating i will soon move her (if i have to get up or something). the tail does say alot about a cats mood, but if you dont look at the whole body you might misunderstand what the tail is saying. take in the ears, the tenseness of muscles, is the cat acting agitated or is the cat purring? cats pur when deeply content...and when in great pain. so yes, the tail can tell the mood of the cat...and no because it isnt the whole story by itself.