Neil deGrasse Tyson claims that 4D beings would be able to see the internal organs of 3D creatures.

“If you're looking at a 2D creature, you can see inside their organs, their inner organs. 2D people can't see, 'cause they have skin, this line- Right. which is their 2D skin, they can't see through the line. But we can see directly into their bodies. So I, I look really ugly to a 4D person.”