This wikipedia article on the "cavity with a hole" model of a black body says:
The hole is not quite a perfect black surface — in particular, if the wavelength of the incident radiation is longer than the diameter of the hole, part will be reflected. Similarly, even in perfect thermal equilibrium, the radiation inside a finite-sized cavity will not have an ideal Planck spectrum for wavelengths comparable to or larger than the size of the cavity.
So I have 2 questions.:
Why is it that light of a wavelength larger than the hole will be reflected?
Why are wavelengths larger than the size of the cavity not emitted?