My bet is that when you dropped the dogs you got some rubbish or thread trapped in there that you can't see and the top thread is snagging on it. Try pulling up the bobbin thread as if you are just starting to sew, and see if you pull anything up with it. If you don't, pull the bobbin thread down underneath again, and pull it up again with the top thread. Sounds monotonous, but this is what I did time and time again last week on a machine because this was the only way I could clear compacted rubbish out from underneath because it was out of sight and out of reach. I pulled up enough fluff to weave a carpet.