Amazon and I are gaming each other. Several days ago I got interested in a video, checked Amazon, and decided to add it to my cart. My total was under $25 (the free-shipping minimum), so I went away until there was something else to add to the cart.
Then I decided I need more NiMH AAs, and so added them to my cart. The total went over $25, so it would have been time to order, except the video price had gone up slightly to top $10. I have a rule that I will not pay $10 for a video; less than that, maybe. So I moved the video into the save for later category and wandered away without placing the order.
The next day, not surprisingly, the video price had dropped back to $9.99, so I moved it back into my cart, and placed the order. The danger here is that Amazon may pin my behavior down too precisely and boost the price of any DVD I place in my cart up to $9.99 if I don't place the order that day.