bait

If we have no other way of catching him, we can always bait our line with the ring.

That angular shadow up yonder was the bait, and we were the hunters.

Have you not tethered a young kid under a tree, lain above it with your rifle, and waited for the bait to bring up your tiger?

There seemed to be no alternative but to catch him red-handed, and to do so we had to use Sir Henry, alone and apparently unprotected, as a bait.