"Expert at Reattaching Limbs" joke

Sam and John were out cutting wood, and John cut his arm off. Sam wrapped the
arm in a plastic bag and took it and John to a surgeon. The surgeon said, "You
are in luck! I am an expert at reattaching limbs! Come back in four hours."
Sam came back in four hours and the surgeon said, "I got done faster than I
expected to. John is down at the local pub." Sam went to the pub and saw John
throwing darts.
A few weeks later, Sam and John were out again, and John cut his leg off. Sam
put the leg in a plastic bag and took it and John back to the surgeon. The
surgeon said, "Legs are a little tougher - come back in six hours."
Sam returned in six hours and the surgeon said, "I finished early - John's down
at the soccer field." Sam went to the soccer field and there was John, kicking
goals.
A few weeks later, John had a terrible accident and cut his head off. Sam put
the head in a plastic bag and took it and the rest of John to the surgeon. The
surgeon said, "Gee, heads are really tough. Come back in twelve hours."
Sam returned in twelve hours and the surgeon said, "I am sorry, John died."
Sam said, "I understand - heads are tough."
The surgeon said, "Oh, no! The surgery went fine! John suffocated in that
plastic bag!"