I think this is interesting.....I shot a mule deer, quartering away at 75yds with a 7STW using 150g Barnes TTSX traveling at +/-3400fps. Bullet entered behind the shoulder, punched a 1 3/4" hole squarely in middle of the heart, busted the off shoulder and came to rest in hide on the off shoulder with the bullet base exposed. The petals were holding the bullet in place. The bullet tumbled at some point to come to rest like that.
The Deer
The Bullet
That's really easy to answer. During the passage of the bullet through the critter, the expansion changes the center of balance of the bullet. The bullet reverses and the base is in front ... basically, the base leads.
The guys at Nosler & Hornady have several photos of bullet bases protruding from the far-side hides.
Hey, it just makes sense.
KD