Actually, there are two types of bully sticks....Merrick's Bully Sticks are NOT penis, they are tendons...even though they are called bully sticks. Other brands (not sure which) are made from penis.
I actually had a problem with the bully stick (penis one). I gave Baby one of the braided kind. She woke up at 2-4am (can't remember now what time) and started gagging and breathing funny!!! She threw up onto my carpet and it smelled BAD!!!!!!

It was the bully stick in the vomit (sorry so graphic) and it smelled like skunk and urine. It was
so disgusting, as her vomit never smelled before (and she rarely vomits). Anyway, I took it away from her and she's been fine ever since. That was over 3 months ago. I won't give them to her anymore. Maybe she was allergic, I have no clue, but I'm not messing with them anymore. BUT...Baby
is the only Yorkie that I know that has ever had this reaction.