Question

flap like loose skin hanging from the neck of an animal

Answer 1

HEY DEAR....
HERE'S THE ANSWER WHICH I THINK IS RIGHT⬇
Many animals have DEWLAP. Some of them are :
Moose, Turkey, Ox, Eland etc.
Any doubts, please ask me in the comments.
I HOPE YOU FIND IT HELPFUL
@ LB :)

Answer 2

Flap like loose skin hanging from the neck of an animal is called a bell or dewlap