Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means melt and this word means to melt something or to melt. You're doing the melting, and you know it because you are the cause (かす) of the melting.
Kyoko(Tokyo accent, female)
Kenichi(Tokyo accent, male)
The thing that you melted in this situation is your toe (と). Feel your toe getting melted away. Augghh it hurts.