An honest-to-goodness genius like Malcolm would know the last book of the standard Christian Bible is "Revelation", not "Revelations". He mis-speaks the name right after the team identifies the symbol drawn in Fr. Reyes' blood on the floor of the chapel.
When Malcolm is attempting to perform the exorcism, and he is repeating Latin phrases after father Pete, the priest says "dominus autem misit ad infernum." Malcolm, however, says "dominum autem misit ad infernum." While the priest's Latin phrase means "the lord sends (you) to hell", Malcolm instead says "(he/she) sends the lord to hell."