Angle cheat glitch
From Worms Knowledge Base
This trick allows you to fire a Longbow vertically. It also works with Baseball Bat if you do not have a Girder.
How To Perform The Glitch
To shoot a Longbow vertically, you have to aim a weapon vertically up and start walking. While walking use the shortcut key (F3) to select Longbow and, while still walking, hit space. An arrow will fire vertically upwards and hit the object directly above the worm. If there is no object above the worm, the arrow will continue rising above the edge of the sky and eventually fall back down onto the worm, usually causing a deduction of health (except in God Mode).
You should hold down one of the walking keys in case, by chance, you get to fire a second arrow and want to make it go vertical also. You can hit space while continuing to walk to fire a second vertical arrow. If it does not hit something within 10 seconds after the retreat time, it will disappear.
In theory, you can also hurt yourself by aiming a weapon vertically down instead of vertically up and doing the same procedure. This will result in an arrow being fired vertically downwards.
In addition, you can do the same thing with Baseball Bat, however, it will not work if you have a girder. When you hit F7 while walking to get to Baseball Bat, the Girder will cause you to stop walking. Hitting F7 again will select Baseball Bat, but because the Girder caused you to stop walking, the Baseball Bat will be automatically aimed out of its vertical position.
Why The Glitch Occurs
There is a hole in the function that stops you from being able to shoot the Longbow up, if you are walking it retains the aim of the other weapon.