It goes click, click, click on its way under the chair… and later on it isn’t there. If it’s possible that it could have left without your seeing it maybe it had a quick nail-clipping session and left going , , ?

If it wasn’t possible to get out from under your chair without your seeing it (eyes in the back of your head, obviously) then it must be nesting in your beard. To paraphrase Mr Lear:

There was a young man with a beard
Who said “it is just as I feared!
While I drank my coffee
The squirrel went dotty
Shrank in size and climbed in my beard.”

You never know.