It happens that some viper's Fangs do shoot out the attack animation if an enemy is on it's attack range (close to left or right), but they never bubble these, while others can hit them when the monsters are more close to their middle. This issue was noticeable a lot on a map where i test spammed these, and deleted the hitting viper's fangs or just the not hitting one.
If enemys are close to other defenses or objects or on slightly tilted or elevated ground, the Viper's Fangs do start their attack animation but are not able to bubble the enemys.
Steps to reproduce:
When the Viper's Fangs shoot, then they also hit and bubble enemys (if it is possible to bubble them).