I normally come home at lunch and check on Bilbo, but I didn't yesterday because I had errands during lunch. When I got home, my husband was there and I could tell he was upset. He said, "We nearly lost him today, honey." I thought he meant that he ran out the door when DH came in, but then I noticed Bilbo didn't have his collar on.
When my husband came in, Bilbo had his lower jaw hooked through his collar and was choking on it. DH said that he thought he was going to die before he got the collar off.
The only thing I can think of was when I put the collar back on him after brushing him I didn't fasten it tight enough. It's leather and has holes like a belt.
Needless to say, I'm retiring that collar and getting one that is adjustable.