Q:

What is the last action?

In the question Why is processing a sorted array faster than an unsorted array?, today I see the active value is today, so I click the [today] and it moves to no-where.
I want to know Why and When clicking on today moves to no-where?
Edit :
I found the list of activities And the fedorqui answer to the list:
Id | Name                             | No-Where
---+---------------------------- ... -+----------------
1  | Initial Title                    | 
2  | Initial Body                     | 
3  | Initial Tags                     | 
4  | Edit Title                       | 
5  | Edit Body                        | 
6  | Edit Tags                        | 
7  | Rollback Title                   | 
8  | Rollback Body                    | 
9  | Rollback Tags                    | 
10 | Post Closed                      | 
11 | Post Reopened                    | 
12 | Post Deleted                     | for reputation < 10K
13 | Post Undeleted                   | 
14 | Post Locked                      | 
15 | Post Unlocked                    | 
16 | Community Owned                  | 
17 | Post Migrated                    | 
18 | Question Merged                  | 
19 | Question Protected               | 
20 | Question Unprotected             | 
22 | Question Unmerged                | 
24 | Suggested Edit Applied           | 
25 | Post Tweeted                     | 
31 | Discussion moved to chat         | 
33 | Post Notice Added                | 
34 | Post Notice Removed              | 
35 | Post Migrated Away               | 
36 | Post Migrated Here               | 
37 | Post Merge Source                | 
38 | Post Merge Destination           | 

A:

This is because it points to a deleted answer: https://stackoverflow.com/a/29942941
If you have >10K reputation you can see it. For those who don't, I have taken a screenshot:

