Deliberately impassive in manner.

synoniemen: deadpan, expressionless, impassive, poker-faced.

Roget 517: unmeaning; meaningless, senseless; nonsensical; void of sense etc. 516.    inexpressive, unexpressive; vacant; not significant etc. 516; insignificant.    trashy, washy, trumpery, trivial, fiddle-faddle, twaddling, quibbling.    unmeant, not expressed; tacit etc. (latent) 526.    inexpressible, undefinable, incommunicable.    ... meer laten zien