first i have to say it, just the last week i saw Ratatouille, when i entered at the cinema, actually i didn’t thought that the movie could be so good or fun like the previous films of pixar… but yeah all started with the so well animation, later the fantastic shots, the exciting adventure… at the moment ( trust me ) i couldn’t breathe, the dedication to do thats rats, thats rats are awsome…you can’t guess what will happen at the end because its a movie so well did, that you never know how ends the history an what can happen with the characters. and oh my god!, that food was so real that im starting to fell hungry and i was eating pop corn!! 
thats my conclusion: nothing can excel Finding Nemo (for me of course), but god it could be my second favorite movie of pixar; and think about it, since 1995 when toy story arrived on theaters until now look the originality and the exciting adventures of each film and dont make talk of the shorts…now im waiting for another master piece, if im right W.H.A.L.E is the next so i dont gonna lose it you can be sure of that… thanks 
