The quest to find whether cryptocurrency bitcoin is in a bubble could be found on search engines, where one bubbly sounding term is on the rise.
Google Trends says the search term "buy bitcoin with credit card" is around its historic peak, notes Nick Colas, co-founder of Data Trek Research and the first Wall Street analyst to take the digital currency seriously.
While the phrase is only about 3 percent of all bitcoin searches, it is on the rise.
The popularity and curiosity of using leverage to get in on the action come as bitcoin's price continues to scale new heights. In another surge to the upside Monday, bitcoin rose past $9,600 in morning trade, a rise of nearly 7 percent in a 24-hour period and 17.5 percent over the past week alone. It later was trading around $9,500.
"These bubbles tend to end in tears," Citadel hedge manager Ken Griffin told CNBC in an interview Monday.