Based on Bill Verners' Inside the Java Virtual Machine, McGraw Hill Companies, 1997

ret - Return from subroutine
  opcode:  169 (0xa9)
  usage: ret index
  stack: No change.
description: Returns to the address held in local variable index.

return - Return (void) from method
  opcode:  177 (0xb1)
  usage: return
  stack before: ...
stack after: [empty]
description: Leaves the method of return type void.