Like drinks. (Emphases below are added, of course.)
According to a police report, the robber ordered a root beer float about 10:30 p.m. at the [Sonic] restaurant in the 1600 block of General McMullen Drive, paid with a $100 bill and told the victim to keep $3 as tip.(from the Express-News)
When the car hop went through his money to make change for a $20 bill at the customer's request, he noticed the $100 bill felt fake and confronted the customer, the report states.
They argued, with the customer pocketing the possibly phony $100, pulling out another $100 bill but refusing to hand it over, and finally threatening the car hop with a knife.
You shouldn't wait until the money feels fake to get suspicious. Anytime anyone orders one drink and tries to pay with a Benjamin, you might want to start considering him with a wary eye. Right away.
You just might.