Weird split problem

Whenever i split i only get the extrusion and bottom surface but it leaves the top part open, I have been trying to do the mouse lesson on level 2 from vimeo. ive never ran into this problem with it before? mouse 2.3dm (1.2 MB)

Hi Jordan- not sure how you are going about this but, in case it helps, here is how I’d do it-

mouse 2_PG.3dm (111.6 KB)