Pope sends first tweet

Flash Points: CBS News National Security Correspondent Bob Orr talks with CBS Senior National Security Analyst Juan Zarate about the "more constrained standards" the president outlined regarding the use of unmanned drone strikes on terrorist targets, exploring what constitutes "sufficient information or evidence" to allow the president to authorize a drone strike under the new guidelines.

Warning: graphic video. A man with bloodied hands and knives appears in amateur video that shows the immediate aftermath of an attack in southeast London in which a man was killed. Jessica Hartogs.

Two men attacked another man near a London military barracks in what British authorities were investigating as a possible terror act. Lucy McDonald reports.

Warning: graphic video. A man with bloodied hands and knives appears in amateur video that shows the immediate aftermath of an attack in southeast London in which a man was killed.

The Popocatepetl volcano near Mexico City continued to show signs of seismic activity last week. Increased explosive activity could lead to increasingly powerful explosions of ash and lava.

A new racing fad in Saudi Arabia has drivers "sidewalk skiing" on two wheels while people cling to the outside of the moving vehicle.