I would like to understand the addition of "$"

Not, "$" but "$!". The exclamation mark is not just for decoration. See perlvar.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re^3: use of $sub by tobyink
in thread use of $sub by JimLS

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