2,734. Vowing by Chulin

Hilchos Nedarim 1:20

If one person tells another, “Secular food, I will eat of yours,” “The secular food I will eat of yours,” “Like secular food I will eat of yours,” “Secular food I won’t eat of yours,” “The secular food, I won’t eat of yours,” “Like secular food, I won’t eat of yours,” it is permitted.

Hilchos Nedarim 1:21

However, if he says: “I won’t eat ritually unclean (offerings) of yours,” “I won’t eat nosar of yours” or “I won’t eat piggul of yours,” it is prohibited because his intention appears to be, “What I will eat will be piggul or ritually unclean, so I won’t eat from what’s yours.”