A monster in the Rogue-style game Nethack, represented by a red 'i'. Though individually a Manes is nearly as harmless as a grid bug, they come in large swarms which can very easily cause YASD. As with most swarms, the best response is to stand in a corridor so they can only come at you in single file.
An important thing to note is that 'Manes' is the singular as well as the plural. This is often misunderstood, understandably.