Slip tool ..
Extract from the manual below ..
“Slipping and sliding events
To help you picture what happens when you slip and slide events, think of an event as a window to a media file. The window can display the entire media file or a small section. When the window displays only a portion of the media file, you can move either the window or the underlying media to adjust the media that is played by an event:
When you slip an event, your event maintains its place on the timeline, but the media file moves in the direction you drag.
When you slide an event, the media file maintains its place on the timeline, but the event moves in the direction you drag.
If you want to slip all of an event’s takes when slipping media, make sure Slip All Takes is selected in the Options menu. For more information, see “Using takes as alternate versions of events” on page 182.
Shifting the contents of (slipping) an event
Use the Slip tool or hold Alt while dragging an event. The slip cursor is displayed.
As you drag the event, the contents of the event shift, but the event will not move. You can use this technique when you want to maintain an event’s length and position, but have the event play a different section of the source media file.
For more information about the Slip tool, see “Editing Tool” on page 19. Slip-trimming an event
Use the Slip tool or hold Alt while dragging the right or left edge of an event. The slip-trim cursor is displayed.
As you drag the event edge, the opposite edge of the event will remain fixed, trimming the media from the edge you drag.