Charles Ellicott Commentary Leviticus 11:31

"These are they which are unclean to you among all that creep: whosoever doth touch them, when they are dead, shall be unclean until the even." — Leviticus 11:31 (ASV)

These are unclean. —Better, these are the most unclean, as Leviticus 11:29. That is, the eight animals so listed are pre-eminently unclean of all the creeping things.

When they are dead. —The phrase, "whosoever doth touch them when they be dead," is simply another expression for "whosoever toucheth the carcase of them," which is used in Leviticus 11:24. Defilement is only contracted when their dead bodies are touched, but not if touched when alive. According to the canon that was in effect during the second Temple, "there is no kind of living creature that becomes defiled while it is alive, or defiles when it is alive, except man only."