He seems very queer sometimes, and even jennie has an inexplicable look. it strikes me occasionally, just as a scientific hypothesis,—that perhaps it is the paper! i have watched john when he did not know i was looking, and come into the room suddenly on the most innocent excuses, and i’ve caught him several times looking at the paper! and jennie too. i caught jennie with her hand on it once. why does the narrator believe that john and jennie are looking at the wallpaper?

The narrator thinks that the wallpaper is having the same effect on them as it is on the narrator.

Explanation:

The strange behavior of John sometimes and Jennie's inexplicable looks made the narrator think that this is because of the wallpaper and the narrator even caught John and Jennie both several times staring at the paper and the narrator also caught Jennie with her hands on the paper. Hence these events lead the narrator to think that they are having the same effect from the wallpaper as the narrator.

answer; the supreme court was placing age in the non-suspect classification category;