Posted by Vel G. on October 21, 2002
I believe this refers to coursing hounds. Greyhound were favored in coursing stag, hare etc. Special collars were used to release the hounds when the game was sighted. (the use of these collars can still be seen at lure coursing trials where Greyhounds and related breeds do simulated coursing as they course a plastic bag instead of a hare). These collars, also refered to as "slip-collars" or "slips" fall quickly off of the dogs neck by use of a special release design so that the dogs have an instantaneous get-away with out having to pull the collar off over their heads (too slow) or running with a collar on (too dangerous). The phrase refers to the excitment of the dogs as they wait to be slipped (released). So that person would be eagerly anticipating action and be excited while contained, perhaps vibrating with anticipation.