A Husband's Claim that his Wife Fraudulently Claimed Virginity: Doubt whether the hymen was lost after they married, plus Doubt she may have been raped: Ketuvot 9a
By "Almanat Eesah" Case: Ketuvot 14a (2 Explanations in Rashi) Doubt whether one entered the Private Property in which there was a Corpse, plus Doubt whether he leaned over the Corpse: Pesachim 10a
Doubt whether a child nursed enough milk to communicate impurity, and doubt whether he consumed it in a short enough period of time for this to be considered significant consumption: Keritot 13a