A soldier is hit by a mortar

These mortars (like most) have an ignition cart in the base that pretty much resembles a shotgun cartridge with a primer.

Around the tail boom are holes to allow hot gases from the cart to ignite increment charges (white disc floppy thing) which are filled with propellant. More increment charges, more range.

In this case the cart fired but failed to ignite the increment charge(s) which are clearly still intact, causing just enough pressure to bloop it out.

The fuse needs a shit ton of inertial force to arm, so it is still safe to handle, no danger here.

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Your classic, "OH SHIT" moment.