I hit a software bug earlier this day and recompiled svn r560 with debug information.
message_add (str=0x7fff8116b000 "The Large yellow snake crushes you.", type=41) at z-msg.c:113
113 messages->tail = m->prev;
(gdb) bt
#0 message_add (str=0x7fff8116b000 "The Large yellow snake crushes you.", type=41) at z-msg.c:113
#1 0x0000000000473bb3 in msg_print_aux (type=41, msg=0x7fff8116b000 "The Large yellow snake crushes you.") at util.c:1451
#2 0x0000000000473cca in message_format (message_type=14595, extra=-20445, fmt=<value optimized out>) at util.c:1585
#3 0x0000000000444dc0 in make_attack_normal (m_idx=43) at melee1.c:443
#4 0x000000000044aeb7 in process_monsters (minimum_energy=100 'd') at melee2.c:3776
#5 0x000000000042a94a in play_game () at dungeon.c:1661
#6 0x0000000000480cd1 in main (argc=3, argv=0x7fff8116c2f0) at main.c:466
(gdb) p *messages
$3 = {head = 0x7f38b0, tail = 0x0, colors = 0x79b260, count = 2049, max = 2048}
I read a "Summon monster" scroll on my last turn.
