HiThe only Danse Macabre I;ve heard of is by Saint-Saens, for orchestra. Maybe you're learning a piano arrangement and the small notes are optional?
I can't believe I didn't work this out the first time I saw it, but some of the notes are wrong if I'm not mistaken. The top G#'s written in the very first incomplete bar should be F# and E# as the lower smaller notes are correct, the top ones are not (as they don't make octaves). Which version is this... I hope there aren't any more mistakes like that.