Sentinels are ranged defenders. Their Spit Neurotoxin ability allows them to instantly stun a potential host from a distance, but their relatively low speed make them more useful to a group of xenomorphs rather than working alone. Sentinels are built for defending the hive, the hosts, and most importantly the Queen herself. Sentinels, not the drones, should be guarding the hosts. Your skillset is made for taking down already infected prey as well as non-infected hosts. Sentinels are for the players that enjoy defence or ambush tactics. Currently you can use Shift+Click to spit on the tile you clicked.