Let's say he has an improper intention to eat something past the proper time that is not supposed to be eaten. For example, let's say the kometz (handful) is burned on the Mizbeach (altar). Let's say he has an improper intention about the kometz—to eat it. He is never going to eat it; it is not edible. Or he intends to burn something that is not supposed to be burned, like the shirayim (the remainder) of the mincha (meal offering), which is supposed to be eaten, not burned. So let's say he has an intention to burn the shirayim past the proper time. In both cases, he is talking about eating or burning something past the time or outside its place, but we are not talking about something that would usually be burned or something that would be eaten. When we say kasher—the mincha is valid—an intention about eating or burning only matters if it is about something that is usually eaten or burned. But if it is about something that you do not usually eat or something that you do not usually burn, the intention is meaningless.
Rabbi Eliezer posel; he disagrees and invalidates the mincha. According to him, the pasuk (verse) about pigul (disqualifying intention) tells us both about eating the part that should be eaten and burning the part that should be burned, and refers to both of them as eating. So according to Rabbi Eliezer, we see that the intentions of eating and burning are basically the same thing. So if you had an intention to burn something that is normally eaten past the proper time, it is a form of eating; the burning is a form of eating. And the inverse: if you have an intention to eat something that is usually burned, that intention also makes it a problematic situation. It is basically interchangeable; it is one and the same: intending to eat something that is meant to be eaten, let's say the shirayim, the remainder, or to burn something that is normally burned, the kometz.
But if the intention was only about less than a kezayit (olive-sized amount) of the remainder, or less than a kezayit of the kometz, we say kasher—the mincha is valid—because eating less than a kezayit is not considered eating, and burning less than a kezayit is not considered a sufficient act of burning. If a person had an improper intention about eating half a kezayit of the remainder and burning half a kezayit of the kometz, or when I pass the proper time, you may think, “You know what? Take the two halves and make a whole, and therefore you have a full kezayit that would be subject to pigul.” We say kasher; the Beracha (blessing) is still valid because in achila (eating) or haktara (burning), mitztarefim: the improper intention of eating and an intention of burning do not combine into one.