Wow, glad you were near by for the rescue!

I have a bunch of those Acu-rites, but mine don't have that clip. I bought mine at Wal-Mart and some at Amazon. All of mine have magnets in the back rather than clips. I reckon they changed it.

Cut or break that clip off if you have not done so already. Sand any rough spots smooth.

if you can't see anything wrong with Henry I would not worry, but would check on him often just in case.

He does have a skull, and since it was Not a blow to the head he is probably ok.

Oviously if you see any neurological issues (balance problems, visible shaking, or you feel tremors) get him to the Vet ASAP.

And don't beat yourself up over this. Now you know how easily they can get into trouble.