Players smack their fists into their palms and count to three before making one of three hand signals: a fist (rock), flat hand (paper) or two fingers (scissors).

玩家们把拳头握在手掌中，倒数3、2、1后伸手做出三种手势中的一种。 三种手势分别为：一只拳头（代表石头），伸开的手掌（代表布），以及两根手指（代表剪子）。

youdao

One of the hands keeps a flat hand shape and it just kind of lightly moves back and forth as if it were a flickering image on a screen."

VOA: special.2011.04.13

This is--If you'll hold out your hand and--one hand flat.

如果你伸出手,手伸平

耶鲁公开课 - 心理学导论课程节选

She holds one hand flat as instructed, the brown carrot there, a gift from the driver.

NEWYORKER: M&M World

We would start to see Proposition 65 warnings on the thousands of consumer products, including automobile and aircraft parts, beer cans, plastic bath and kitchen appliances, cell phones, cameras, flat screen television sets, hand held computing devices, that use BPA to improve their safety and performance.

FORBES: Fear-Mongering, Junk Science And NRDC

Each piece starts with a flat wooden base and a core of hand-sculpted Styrofoam.

WSJ: If Kids Can Play, Will Mom Shop?