From Valve Developer Community
- Tests the entity that called the input (the
!activator) against the filter, and fires either the
Bug: Calling this input will cause the server to crash if the
!activatorentity no longer exists. Do not use this input to test any entities which may be asynchronously deleted, such as players or projectiles, or in an i/o chain which might be initiated by entity deletion, such as the
OnEndTouchoutput of a trigger.