wrote
Martin Brown wrote
tabbypurr wrote

I need to capture a half-feral cat with a serious medical problem.
I have a large wire cage that's not designed to be used as a trap.
If I tie string/rope to the open door, pass it through the wire cage
and run it along the ground, it would be possible to wait and pull
the string once the cat enters. This won't work unless the door closes
and at the same time a knot ties it shut. The knot needn't hold long,
10 seconds against a large strong cat should do the job. Question is,
what knot should I use?

You need to arrange that as the door closes something else locks it -
a piece of bent garden wire or length of metal would be my choice.

I think something is missed there.

By you, yep.

For the cat to enter, people need to stay a fair distance away.

Yep.

That means the string would have to hold against
a strong and very frightened semiferal cat,

Nope, not if there is a proper latch on the cage door
that only needs minimal force from the string to see
the door latched. Then the string is irrelevant after that.

Even without a latch, a decent length of cord will hold the
door closed fine if tied off where the person sits and pulls
the door closed, while that person goes to the cage once
the cat is in the cage to secure the door at the cage.

But more skill required by the person, but not much.

despite being pulled from a long way away.

Doesnt matter how far away it is within reason.

I don't see that working.

It will anyway.

Just borrow a cage from the RSPCA, they clearly do work.