To unlock this trophy:
1. Load up the heart transplant level
2. Cut the rib cage out in one whole piece, (would advise using the surgical saw)
3. Pull the whole rib cage out of poor Bob
4. Success, trophy unlocks
If patient (Bob) starts to bleed out hit him with the blood clot needle. Take your time. Good luck =)
Attached is a video detailing the trophy, credit to The Gamer With Kids.