When frying foods, your oil's temperature can mean the difference between perfectly crisp foods and soggy ones. Although you can use a grain of rice or a wooden spoon to see if the oil is ready, you'll probably have one ingredient already out to test the oil: breadcrumbs.
Drop a couple of breadcrumbs into the oil. If they sink, the oil is not hot enough. If they quickly burn up, the oil is too hot. But if they bubble and float to the top, the oil is just right and it's time to fry.
I learnt this tip while watching Giada De Laurentiis make rice balls on TV, but I couldn't find an online post with the tip associated with her. The panko cooking instructions below from Yutaka, however, also encourage us to check hot oil with breadcrumbs (Japanese or not).
PANKO Japanese-style breadcrumbs [Yutaka]