unusual

Yesterday,my grandmother cooked a chees cake.It looked so delicious and smelled good! It seemed that I saw such a sweet food for the firsttime in ages because I was busy with study last year. I wanted to eat it,but I couldn't because of flu... I am going to eat today.So my brother had a slice of the cake alone.But,as soon as he had a bite, he drank water. I asked,"What's the matter?"He said ,"a littel sour..." " I mistook sugar from salt!" my grandma said smiling.It was very unusual that she mistook because she is very good at cooking.