Postmortem plant question here: had this little pincushion cactus for several years before recently it shriveled up into a tiny ball of spikes. After about a month I finally accepted that it had died, and decided to clear out the pot. When I went to uproot it, the spike ball popped off and I got a good look at the inside. It look like it had been hollowed out and filled with sand? The substance was a little clumpy, and kind of reminded me of an anthill— I wish I got a photo. Not sure if that’s normal, or if I accidentally subjected my cactus son to some unknown horrors. Anyone know what that was?