But how is that possible?

This requires GD and will make a file called o.png in the directory from which it is run.
It is based on the "father of the impossible figure" (see what i did with the title now :) ) Oscar Reutersvard's most famous piece,
For those without GD you can see the output here 

$_=q^use G;$i=M G::Image(FABL0,L0,L0);J l{$p=M G::C;$$_=ord(D-Lfor qw.
+x 
y.;$p->addPt(($x+=D,($y+=D)while$#_;AfilledC($p,D}J d{E0,0,L,-HL,H-L,H
+AB
KFEL,HL,-H0,L,-L,HABL,0,0)}J a{d@_;E0,0,0,L,L,H0,-L,ABL,F}$_="]]?l!{!]
+!?
!!?0]?{N";s#(.)(.)#a"$1","$2";\n#g;/".+;/;$_.="d$&";eval;open Z,">o.pn
+g"
;binmode Z;print ZApng^;for$r(qw.$i-> colorAllocate( Polygon shift) l@
+_, 
KK); GD 10, I sub 153, 20 new.){$l=chr 65+$c++;s#$l#$r#g}s#\n##g;eval

[download]
enjoy
al

UPDATE as per Pied's request, a deobfuscated version is available here, with an explanation of what's happening and the obfuscation process...
Update 2 changed link to output as old server is b0rked

In reply to Bear is driving? by teamster_jr

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