If the task you have just popped has a question mark at the end, you will be prompted to make an observation. See Observations for more about observations.
(This behaviour is controlled by the variable
sidebrain-auto-ask-info-gathering-results; it happens if it is
non nil, and contains a regular expression describing
information-gathering tasks.)
If the task came from a “to do” comment, the word todo in the
comment is changed to done. this behaviour is controlled by the
variable sidebrain-mark-done-comments.