In the "proposal scene," when Joey closes the door, it does not latch, but the sound of a latching door is heard. Joey has to close it again, but then, no sound is heard.
At the end, when Chandler walks into the apartment full of candles and Monica is standing there, you can clearly see the stage lights up above.
At the end when they are all hugging in celebration, Phoebe says it isn't right because Ross isn't there. Rachel replies, "Oh, hell, he's done this three times, he knows what it's about!" But, of Ross' three marriages, he only proposed to Carol and Emily. Rachel never received a proposal, since she and Ross were married in Vegas while drunk.