Introduction and Physical Description
Aspises are serpents or dragons found in medieval European mythology  probably based on the characteristics of the aspic viper (Vipera aspis).  The singular form is Aspis, and the name means 'serpent.' 
European folklore presents varying descriptions of the Aspises. Some claim they are smaller than a full-sized dragon with two feet and wings;  others state that they are quadruped dragons with wings. 
All resources on the Aspis agree on one element of the species: Aspises are highly poisonous.  An Aspis is so poisonous that touching its skin, even the skin of a dead one, would be fatal.  The bite of an Aspis causes instantaneous death. 
Defending Against the Aspis
There is one sure method for avoiding an attack by an Aspises; they are distracted or entranced by music.  Many Aspises are aware of this particular flaw, so they developed a defense mechanism to dull their sensitivity to music. 
The Aspis is often depicted in this music-dulling position, with one ear to the ground and the other ear stopped with its own tail.  Even when the Aspis managed to stop the entrancing effects of music on itself, it also enables anyone nearby to escape. 
For more information on footnotes and references, please see the bibliography.