Throughout the series of Portal, you are taught that you cannot place portals on any moving panels. If a portal is previously placed on any moving panel, it will be destroyed.

BUT, did you know that there is only one time in the entire series where this rule does not apply? Have you guessed it? While you are escaping with Wheatley, you have to use a laser to destroy her neurotoxin pipes. But in order to do so, you must place a portal on a moving panel so the laser can cut through the pipes.

2 words, Valve;

Lo

Gic