sentences:  In that case, the bubble is implemented by feeding NOP ("no operation") instructions to the execution stage, until the bubble is flushed past it.The following is two executions of the same four instructions through a 4-stage pipeline but, for whatever reason, a delay in fetching of the purple instruction in cycle #2 leads to a bubble being created delaying all instructions after it as well.The below example shows a bubble being inserted into a classic RISC pipeline, with five stages (IF = Instruction Fetch, ID = Instruction Decode, EX = Execute, MEM = Memory access, WB = Register write back).