Chandler finds some racy pictures of Monica's grandmother and shows them to Monica. Moments later, Erica comes in and Chandler takes the photos from Monica. The camera changes angles and the photos have now disappeared from Chandler's hands.
At around 06:00, the Twin Towers can be seen.
Chandler finds the handcuffs pretty openly on the top shelf of the closet. There is no way nobody has seen them before.
When Rachel says to Ross "I cannot believe that after ten years, you do not know one thing about me" they've known each other since high school therefore they've known each other for more than ten years.