The verification may be omitted when an admission of the truth of the allegation might subject the party to prosecution for felony. No pleading can be used in a criminal prosecution against the party as proof of a fact admitted or alleged in it. (C.C.P., s. 117; 1868-9, c. 159, s. 7; Code, s. 258; Rev., s. 493; C.S., s. 533.)