Texas Chainsaw costume question?

Sally Hardesty (Marilyn Burns) and her wheelchair-bound brother Franklin (Paul A. Partain) travel with three friends to a cemetery holding the grave of Hardestys' grandfather. They aim to investigate reports of vandalism and corpse defilement. Afterward, they decide to visit an old Hardesty family homestead, and on the way, the group picks up a hitchhiker (Edwin Neal). The man speaks and acts bizarrely, and then slashes himself and Franklin with a straight razor before being forced from the group's van. The group stops at a gas station to fuel their vehicle, but when they find out from the proprietor (Jim Siedow) that the pumps are empty, the group continues to the homestead, intending to return to the gas station later after a fuel truck makes its delivery. Franklin tells Kirk (William Vail) and Pam (Teri McMinn) about a local swimming hole, and the couple heads off to find it. Instead, they stumble upon a nearby house. Kirk decides to ask the residents for some gas, while Pam waits on the front steps.