It's common knowledge that cats and boxes go together.
And cats will make an effort to get into just about any box, no matter the fit.
June may think she is a "small" cat.
And yes, this is a "small" box. And yes, she did get into it.
However, I do wish to point out that she is definitely on the medium size,
heading toward large, which is why she is on a diet!
Take a look at the last photo, bottom right. This is the expression I got
when I reminded her that she is not small, and that she
is on a diet, and if she does not adhere to it,
soon she will not fit into any boxes at all!
Her bruised ego was repaired a bit when
I assured her she was absolutely a prime cat.