If you have half a mind to join the Hash, that's all it takes. If you have hashed before you will know the format but for the newcomers here's a quick rundown on what happens.
The Hash generally meets at a pub chosen by the HARES and the HOUNDS set off at the appointed hour along a clearly defined trail (blobs of chalk or sawdust) with the front runners calling "ON, ON" for the benefit of the slower runners and latecomers catching up.
Every 500 metres or so the trail will end signified by a check mark which may be in the form of a line or a circle - ask the hare before you set out. The frontrunners on reaching the check start searching for the new trail.. This can start up to 50 metres from the check in any direction. The time taken by the frontrunners to find the new trail allows the runners at the back (the "social or chat-pack") to catch up thus increasing the chances of everyone reaching the the pub at the end at roughly the same time. The frontrunners will usually find that the cunning hares have laid some FALSE TRAILs in addition to the the real trail - these falsies usually consist of up to 3 blobs followed by an X or a T (again ask!). This ensures that the really fit types, known as FRBs (Front Running Bastards) will become exhausted more quickly and be forced to join the social pack. Another device used by Hares to achieve the same objective is the LOOP whereby the trail might go round 3 sides of a field allowing the back markers to run across the fourth. Hash runs are usually 4 - 7 miles long and are designed to last 1 - 1½ hours. Revelries in the pub after the run are up to the individual but it has been known for some muddy sweaty hashers to be turned out of the pub at closing time...
To get an idea what happens on a hash trail have a look at the Mendip Hills H3 Hash Player where the routes actually taken by hashers on the trail can be replayed. See the regroups, false trails, SCBs and FRBs. Watch how the lead changes constantly as an FRB becomes lured down a false trail.