You asked the right guy

. I worked in a meat packaging factory for 4 years (then became a sys admin, go figure

)
I worked in chopping for a few weeks and spent mucho time making the smokie "mixture". If I recall correctly the recipe is the following :
15lb low grade pork
20lb emulsified skin
20lb shredded beef heart (that was a fun job, I got covered in blood and looked very scary

)
15-20lb rework (rework is stuff that falls on the floor in the packaging area)
+spices
Rework is actually fine... stuff that falls near drains and dirty areas got sent to tank where it became dog/cat food.
Most rework is actually pieces that don't look as good, or can't be sliced properly because of their shape.
God I miss those cryovac/tiromat days

.
<edit>bolded the ingredients for more effect

</edit>