Once the bullet or ball flattens, the opposite hide kinda acts like a catchers mitt...It can actually strech away from the body and absorb the flattened projectile....Mushrooming is good as it leaves alot of damage on the inside...Alot of variables come into play once it hits a deer...as we all know, a bullet that doesn't mushroom and exits can be bad business, as well as one that opens too quickly...Its sorta a catch 22...We all want exit wounds for better tracking, but a bullet that does more damage inside a deer will usually drop them faster...And even if you have an exit, you can't be sure that you will have a blood trail....That's where confidence comes in, you must know that you hit the deer properly so you will look longer and recover the deer.