hoax 是一个可数名词,跟trick 是近义词,所以是play a hoax,表示捉弄

hoaxes复数

英[ˈhəʊksɪz]

美[ˈhoʊksɪz]

n.

骗局;恶作剧;

v.

捉弄;欺骗;

例句

They were the victims of a cruel hoax.

他们成了一大骗局的上当受骗者。