Wearing a poker face: studiously neutral; giving nothing away.(adjective)
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Use "poker-faced" in a sentence
"So Paul stood up and nodded formally at Roz Woodman, ushering her out the door, his expression poker-faced, his body clenched tight."
"Why we like him: Stunned Man (2004) features a dizzyingly brilliant absurdist slapstick routine in which a poker-faced guy destroys his apartment, dives into the bathroom mirror and reappears through the door to begin the whole process afresh."
"To some he's a prankster cracking poker-faced one-liners, but to others his cross-examination of art-making is inspired, delightful and provocative in equal measures."