What do you do?

I'd look around for pranksters, then stick just my head through to scout out just in case. If it was a portal and I could see it from the other side and could breathe I'd probably give it a go.

Throw a stoat through first, Ben- at least a cat...

No animals were hurt in the making of this post.
 
Throw a stoat through first, Ben- at least a cat...

No animals were hurt in the making of this post.
Yes, but if they just disappeared then I'd still be none the wiser. I would just have thrown an animal into a hole! And if they didn't disappear, then I'd just be critter chucking and that's no good to anyone or them. The way I see it, is that there are times when if you want to know if a drink is any good or will kill you you just have to drink the thing and have done with it!