Czech man and soviet agent

Back in the unhappy days when Czechoslovakia was under Soviet
domination, a valiant freedom fighter was wandering through the
countryside, trying to evade a Soviet agent, who was in hot pursuit,
found himself near an old castle, and went inside for refuge.

Soon he found that the Soviet agent had followed him into the castle so
our hero slipped into the nearest hiding-place, which was a medieval
armor. He remained there, very still, until the Soviet gave up in
disgust, and left him free to continue working for the liberation of his
native land.

Why didn't the Soviet agent think to look inside the armor?

"Very simple,... As a well-trained Marxist, he would never consider any
capitalistic lie as that there was a Czech in the mail."

* Czech = sounds like cheque
Mail = kind of medieval armor