The turkey made of paper that Phoebe brings and sets on the table keeps changing directions. Sometimes the head of the turkey is pointing towards the TV and sometimes the head is pointing towards the kitchen.
When Monica suggests that Ross should try the trifle, his plate is already half eaten. Immediately after, it's untouched again.
Ross goes from having some whipped cream on his lip/chin to not between shots after he shovels the rest of the meat trifle into his mouth and wiping with a towel.
As Joey is eating Rachel's trifle, the amount of trifle on his plate gets smaller then bigger then smaller again between shots.
If Rachel were making a trifle she wouldn't have started the day of, as the recipe would have noted it would need to be refrigerated for eight hours after being prepared. Though this could be construed to her confusing the second half of the recipe with a shepherd's pie.
When Ross unstuck the pages, Ross turns over the page and discovers that Rachel made part of a shepherd's pie. Rachel would have noticed that she made a mistake because the beef was in the middle of the trifle, she would have had to have flicked back to the previous page to continue with the recipe.
Phoebe manages to go to Rachel's room, fall asleep, have a long-winded dream, wake up, and come back out, all in around two minutes.
When Jack Gellar says that he knew Monica broke the porch swing, in the background you can see the edge of the set and "spike tape" used to show the correct position for set pieces, actors etc, and what appears to be the end of the set that would be Rachel's old room..
When Rachel makes the trifle including a layer of beef sautéed with peas and onions, Ross says she made half a shepherds pie. Shepherds' pie isn't made with beef, it's made with lamb. Cottage pie has beef.