Remus made an involuntary glance at Selina when she whistled for the taxi. That was pretty cool! He could never learn to do that, much less whistle without fingers in.
It was only when the taxi finally came into view that Remus realized he had no idea how to pay for it. He didn't bring any muggle money with him and he rather doubted the driver would accept wizard currency. As it was late, though, he figured he might be able to fool them into accepting a few sickles and knuts since they look like silver and bronze muggle coins, anyhow, but he swore he heard something about a protective charm around them that prevented them from being exchanged with muggles.
This was what went around his mind as the taxi came to a stop and Selina was writing something. In the end, he decided that if he really couldn't help it, he'd just cast a confusion charm on the taxi driver and beat it and hope that he'll be forgiven for his actions. Desperate times call for desperate measures, after all, didn't they say?