Mastercard (MA -4.5%) and Visa (V -3.6%) stocks drop in Monday trading, both backtracking from strong gains on Friday. An interesting note, though, on Friday Strike's CEO discussed how the company's app uses bitcoin (BTC-USD) as a "standard under the hood" to allow consumers to tip anyone around the world. On Sept. 23, Twitter said it will use Strike to allow users to pay tips with bitcoin. In an interview on CNN, Strike CEO Jack Mallers said the cost of transferring money through apps such as Strike can go to "zero". Card processors charge 2.5% because of their legacy costs and intermediaries, he said. "Instead of a large retailer paying 2.9%, we can charge them 0.05% if we want," Mallers said. "It's all cash profit." He points out, though, that Strike isn't "getting around" any regulations. The company is a regulated entity and takes it very seriously, he said. Other payment